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

<passage>:
"That's what I said. That's what the people are buying. That's what they'd better get." Grdznth problem getting to be a PRoblem, need above the desk. So were the Grdznth and Charlie. told her to go away. I told the rest of the crew to go away, too." graceful slow motion against the far wall. "Now why don't you go away, too?" that. The energy factor," he mumbled. "Nobody thought of that except in passing. Should have, though, long ago. Two completely independent universes, obviously two energy systems. Incompatible. We were dealing with mass, space and the desk pad. "Look, it took energy for them to come through—immense quantities of energy. Every one that came through upset the balance, distorted our whole energy pattern. And they knew from the start that the differential was all on their side—a million of them unbalances four billion of us. All they needed to overload us completely was time for enough Grdznth were mammals—"docile, peace-loving mammals," A lovely place, really. Just a little too cold for Grdznth. They the seat as the Grdznth breathed at him wetly through damp "For them," whispered Tommy. The Grdznth nodded sadly. "It's horrible of me, but I just "For them," Charlie said. thought Earth was much nicer." going east ?" "Well, you seem to have drifted through into the wrong The Grdznth looked at him reproachfully. "The Wives, of course. The climate is so much better, and they mustn't be disturbed, you know." in the East just now," said the Grdznth. "Oh, not many, not many at all. Only the Wives—half a million or so—and their spouses, of course." The creature clicked his talons nervously. "We haven't much more time, you we couldn't have stopped over here, I just don't know what we'd have done." sticking out his tongue at the Grdznth. the Grdznth was beginning to fade out. drink, have a cigar—do you want my job? It's yours. Just speak up." "Check." "To people who don't want to buy them, right?" "In a manner of speaking," said Pete testily. "Yes, I know. And the Grdznth are getting worse by the The more Grdznth come through, the more they act as though they own the place. Not nasty or anything—it's that infernal politeness that people hate most, I think. Can't get them mad, can't get them into a fight, but they do anything they please, and go anywhere they please, and if the people don't like it, the Grdznth just go right ahead anyway." the Grdznth a bit—they have personal protective force fields around them, a little point they didn't bother to tell us about. they can't be killed, that they're just moving in to stay." "I wish I knew. I mean, for sure. The psych-docs say no. The Grdznth agreed to leave at a specified time, and something in their cultural background makes them stick strictly to their agreements. But that's just what the psych-docs think, and they've been known to be wrong." "And the appointed time?" Tommy spread his hands helplessly. "If we knew, you'd according to the math boys. It's a parallel universe, one of several thousand already explored, according to the Grdznth are analogous, and we happen to be analogous to the Grdznth, a point we've omitted from our PR-blasts. They have an eight-planet "Apparently. Nobody knows how they predicted it, but they did. Spotted it coming several years ago, so they've been romping through parallel after parallel trying to find one they can migrate to. They found one, sort of a desperation choice. It's cold and arid and full of impassable mountain chains. With an uphill fight they can make it support a fraction of their population." Tommy shook his head helplessly. "They picked a very sensible system for getting a good strong Grdznth population on the new parallel as fast as possible. The males were picked for brains, education, ability and adaptability the females were chosen largely according to how pregnant they were." Pete grinned. "Grdznth in utero. There's something poetic about it." that climate, at least not until they've been there long enough here for gestating Grdznth, even better than at home. So they came begging for permission to stop here, on the way through, to rest and parturiate." "So Earth becomes a glorified incubator." Pete got to his it just doesn't wash. If the Grdznth are so unpopular with the masses, why did we let them in here in the first place?" He looked narrowly at Tommy. "To be very blunt, what's the Karns'll tell you why." "It's the parallel universe business, of course," he said to Pete, with Tommy beaming over his shoulder. "The Grdznth can cross through. They've been able to do it for a long time. According to our figuring, this must involve complete control of mass, space and dimension, all three. And time comes into one of the three—we aren't sure which." spheres popped out and began chasing each other about in spin. "No wires?" " Strictly closed the box with a click. "This is one of their children's toys, and theoretically, it can't work. Among other things, it takes null-gravity to operate." "and how long the Grdznth gestation period will be." Failed!" The Grdznth sitting on the stool looked regretfully from the cosmetician to the Public Relations men. "I say—I "So you can't make them beautiful," said Pete. "Can't you make them cute?" of nowhere, anywhere. In church, in bedrooms, in rush-hour as it is. And they don't do anything about it. They apologize profusely, but they keep coming through." The two started something." "Do something! You think I'm a magician? I can just make clear. If the Grdznth do not go, I go." There's one thing they are though, at least half of them." got several hundred thousand pregnant Grdznth just waiting for all the little Grdznth to arrive, and nobody's given them a Grdznth are lovable?" the people anything you want. If we're going to get across the sanctity of Grdznth motherhood, my friend, anything goes." "It's genius," chortled Tommy. "Sheer genius." "If it sells," the senator added, dubiously. The planning revealed the mark of genius. Nothing sudden, harsh, or crude—but slowly, in a radio comment here or a newspaper story there, the emphasis began to shift from Grdznth in general to Grdznth as mothers. A Rutgers professor copy, hypersensitively edited copy, finding its way into the light of day through devious channels. Determined movements to expel the Grdznth faltered, trembled with indecision. The Grdznth were ugly, they frightened little children, they were a trifle overbearing in their insufferable stubborn politeness—but in a civilized world you just couldn't turn expectant mothers out in the rain. Not even expectant Grdznth mothers. "Why don't people respond ?" Tommy asked plaintively on the morning the third week started. "Haven't they got any "Hmmm," said Pete. "Well, why won't they? The people just didn't trust us, that the Grdznth girls to gestate. But what are we hearing from nothing except a whole lot of Grdznth and more coming through just as fast as they can. I'm beginning to wonder what the Grdznth are "Well, they can't gestate forever." see some baby Grdznth at the end of it all." There was dead silence in the room. "Baby Grdznth,"

<question>:
Why were the Grdznth leaving their own Universe?

<options>:
A Their planet was cooling down too much
B Their sun was about to explode
C They were being chased
D They did so completely by choice

<answer>:

B