Read the following passage and questions, then choose the right answer from options, the answer should be one of A, B, C, D.

<passage>:
"These donors were dead, but you can be thankful we had parts of their brains available." Crander delved into the file and came up with a "Here are some body part contributors." He read rapidly. "Dimwiddie, Barton, Colton, Morton, Flam and Carnera were responsible for arms and hands. Greenberg, Rochefault, Gonzalez, Tall-Cloud, Gowraddy and Tsin highly attractive—but surely he ought to have known that long ago. "Of course—a replacement. I told you it was a serious accident. They had to use whatever was handy." "I suppose so—but shouldn't they have tried to stick to the original a smashup," he said. "You'll have to expect some lapses." "I'm making allowances. But can't you tell me something about myself?" He had been seriously injured and he was still weak from the shock. He the proportions differed from one side to the other. His knees didn't match. Be-dum, be-dum, be-dumdum, but your knees don't match —the What were they, a bunch of humorists? Did they, for comic effect, piece together a body out of bits and scraps left over from a chopping block? It was himself he was looking at, otherwise he'd say the results were neither hideous nor horrible, but merely—well, what? Ludicrous and an involuntary clown, a physical buffoon that Mother Nature hadn't she began dressing. There was quite a contrast between the loveliness of her body and the circus comedy of his own. "Difficult, isn't it?" she said, tugging her bra together and closing generally, though not around the chest. It was difficult and in addition to his physique there were the memories he couldn't account for. Come to think of it, he must have first corollary of the theorem. The second is that there are critical times in the recovery of the patient. At such times, with the least and carry them through by himself, even though running a slight risk of physical complications." "That's new, isn't it?" she said. "I always thought they watched the patient carefully." It ought to be new—he'd just invented it. "You know how rapidly initiative is more important than perfect health." skill. He wanted to protest, but didn't. Maybe it was the hand she was holding—it seemed to be equipped with a better set of nerves than its Even if he was sure, he didn't know whether he could tell her—and he wasn't sure any longer, although he had been. On the physical side of marriage, how could he ask her to share a body she'd have to laugh at? "Wysocki's theorem," he told her. "The patient has decided to walk." "The director—Doctor Crander. I don't have an appointment." "Glad to see you," said Doctor Crander, behind the desk. He was nervous Doctor Crander tried to fight his way through the desk. Being a little wider and solider, though not by much, the desk won. He contented The doctor came cautiously around the desk this time. "Of course. I Crander frowned, his nervousness rapidly disappearing. "Then it was They had underestimated him, but he didn't mind. Of course, he didn't Without waiting for him to comply, Crander pushed him into a chair and his bewildered patient. Finally Crander seemed satisfied. "Excellent," he said. "If I didn't Merrol wasn't as pleased as the doctor appeared to be. "Granted you can Crander eyed him clinically. "We don't ordinarily do this—but it is Miss Jerrems flashed a glance of open adoration at the doctor and was not wholly true—Crander didn't seem much affected. But he was a doctor and used to it. Furthermore, he probably had room for only one emotion at the moment—relief at the return of his patient. mass of records. Crander noticed his expression and smiled. "You're our prize case, Merrol. I've never heard of anyone else surviving such extensive surgery. Naturally, we have a step-by-step account of everything we did." Crander dug into the files and rooted out photographs. "Here are pictures of the wreckage in which you were found—notice that you were strapped in your seat—as you were received into the hospital—at various stages in surgery and finally, some taken from the files of the Merrol winced. The photographic sequence was incontrovertible. He had to standard methods. One cell won't do it, ten yield an uncertain identity—but as few as a hundred cells from any part of the original body, excepting the blood, constitute proof more positive than fingerprints before the surgical exchange of limbs. Don't ask me why—no one knows. But it is true that cells differ from one body to the next, and this test detects the difference." The mass-cell radiographs did seem identical and Dr. Crander seemed "You did a fine job," he said. Recalling the picture of the wreckage, Crander's eyebrows bounced up. "We're amazed at how well we have The doctor seized it. "Beautiful, isn't it?" Crander waggled it gravely. "It coordinates perfectly. I've observed The other just didn't understand. "But the size—it doesn't match my arm!" "Doesn't match ?" cried the doctor. "Do you have any idea of the biological ways in which it does match? True, it may not be esthetically harmonized, but here we delve into the mysteries of the human organism, and we can hardly be striving for Botticelli bodies and Michelangelo men. First, your hand moves freely at the joint, a triumph of surgical skill." He moved the hand experimentally, to show Merrol how it was done. He dropped the hand and hurried to a screen against Crander drew his finger across the surface and the mark remained. "You other factors just as potent and far more complex." He scribbled meaningless symbols on the screen with his finger. "Take the bone factors—three. They must be matched in even such a slight contact as a joint ... this was done. Then there are the tissue factors—four. Tendon factors—two. Nerve-splice factors—three again. After that, we move into a complex field, hormone-utilization Dr. Crander seemed about to pluck one of Dan's eyes from its socket. "Surgical and growth factors involved in splicing a massive nerve bundle pass any layman's comprehension. There are no non-technical terms to describe it." It was just as well—Merrol didn't want a lecture. He extended his do something with this? I don't mind variation in thickness—some of that will smooth out as I exercise—but I'd like them the same length." "There were many others injured at the same time, you know—and you were one of the last to be extricated from the ship. Normally, when we have to replace a whole arm, we do so at the shoulder for obvious reasons. But the previously treated victims had depleted our supplies. Some needed only a hand and we gave them just that, others a hand and Crander stared at a crack in the ceiling. "Further recovery will take could do for him until it was too late. How long could he expect Erica to wait? The doctor hadn't finished the medical session. "Replacement of body parts is easy, after all. The big trouble came when we went into the brain." "How hard do you think your skull is?" Crander came closer. "Bend your Merrol obeyed and could feel the doctor's forefinger slice across his Crander traced out five areas he could feel, but not see. "Samuel lepidopterist—Duke DeCaesares, wrestler—and Ben Eisenberg, authentic, but they weren't his—nor did the other wives belong to him. It was no wonder Erica had cringed at their names.

<question>:
Why was Dr. Crander so proud of his work on the patient?

<options>:
A They were able to rehabilitate Dan much more quickly than expected.
B No one had ever spent that extreme amount of time in a regeneration tank before
C They thought the patient would never walk or talk again.
D Overcoming the complexities involved in matching donor body parts.

<answer>:

D