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

<passage>:
blastoff. Sanchez asked. There was nothing to do but turn back to Rathole and see if Jan smiled a tight smile. claimed descent from William to prove it, but on Venus there was no one who could disprove it, either. out," he said. "Since we have no fuel, we may as well have no engines." of Orange. He had no genealogy before blastoff time. Jan needed all his Dutch stubbornness, Everything was ready, except climbing aboard, closing the airlock and pressing the firing pin. What on Venus could have happened to Van Artevelde? The last Jan was at a loss to know how radio message they had received, he and the patient took off successfully and Jan bounced against his in an aircraft. What more than an hour ago, had said Jan felt justifiably exasperated "It isn't a colony, in the sense "An effort was made," replied Sanchez quietly. "Perhaps you do Jan mentioned this to the groundcar radio. "That's the third time in half very sincerely that the big blond Jan incredulously. three times." "Don't worry," said Jan. "I'll be back on time, with a broom at the masthead." And Van Artevelde had promised to come back triumphant, with a broom at his masthead! reaction, considering the scarcity of brooms on Venus. "Mmm," grunted Jan. He Ours are powered like that, but we cannot operate them when the eyes returned Jan's glance. "If the disease has just started, the boy could wait for the next Earth ship, couldn't he?" asked Jan. "I said I had just diagnosed it, Heemskerk wore a spacesuit. señor ," corrected Sanchez. "As you know, the trip to Earth takes 145 days and it can be started only when the two planets are at , scheduled to begin an Earthward orbit in a few hours. the right position in their orbits. Have you ever seen anyone die It was near the dusk of the sweeping from the comparatively chill Venerian nightside into "Yes, I have," replied Jan in a 485-hour Venerian day, and the the superheated dayside. Oostpoort, began to settle nearby, and there was Van Artevelde leaning over Jan had just figured out a combination arrest and cure the disease was removal from the dry, cloud-hung surface of Venus and return to a moist, sunny climate on Earth. Without that treatment, once the typical mottled texture of the damned thing ought to get here "Jan!" boomed Heemskerk, Earthship over at Rathole." "Rathole?" repeated Heemskerk. "What's that? I didn't Jan struggled to his feet and within two thousand kilometers." wait for a later ship, if his life is to be saved. He must get to Earth at once." Jan puffed at the Heerenbaai-Tabak and cogitated. The place when the colony folded several years ago. It's about eighty kilometers away, right across the bunch of laborers left behind pronounced. "The "Had no fuel," replied Jan "I can find one. And we'll have to hurry for blastoff. But, first, what happened? Even that expense of sending the boy across the millions of miles to Earth by spaceship. "Who's paying his passage?" he asked. "The Dutch Central has to blast off in thirty hours to catch Earth at the right orbital spot, and the G-boat has to blast off in ten hours to catch the Vanderdecken to wait for the next ship," he "This passenger can't wait," said Dekker. "He needs to be evacuated to Earth immediately. He's suffering from the Venus Shadow." "Certainly," replied Jan with Jan whistled softly. He had Jan relit his pipe silently, making "Jan, you're the best driver in Sanchez. good mechanic," answered Sanchez, glance at Jan's face. "He has Jan grunted. land. But if you have any sort of aircraft here, it might make it whose crust was peculiarly subject to earthquakes, particularly at the beginning and end of each "I'm afraid not," said Sanchez. long day when temperatures of a thin fault area of a planet "Wait," said Sanchez, lifting just right. The three earthshocks that had shaken Den Hoorn since he had been driving made his task no ...." "I know them. I've operated them, before I left Earth. Man, you don't expect me to try to fly one of those little things in this an Earth-day. The thermometer showed the outside temperature to have dropped to 40 degrees Jan. "But you know I'll do it." Sanchez looked into his face, "I was sure you would be willing," and came to them. As Jan arose, land. After a moment's hesitation, he swung the groundcar northward ," she murmured. " Un Jan disengaged himself gently, flying trips back over here in his leisure time. Language barriers were not impassable, and feminine Sanchez was tugging at his height returning eastward. The ground heaved and buckled like a tempestuous sea. groundcar upright. Then, in unison, both earthquake and wind died to absolute quiescence. Jan made use of this calm to Jan sighed. It was an unhappy asked Sanchez. Sanchez smiled ruefully, as he had once before, at Jan's appellation used on terrestrial railroads? was carried back to the flat lands around 's Gravenhage. For ," he said, turning back to Jan. "The Americans, of Jan thought that over, trying clean again. There was no one moving abroad, but just inside the community The groundcar! Jan straightened and snapped his fingers. "Doctor!" he explained. "Send a couple of men to drain the rest of the fuel from my groundcar. Sanchez gave rapid orders in and outside. As soon as they reached ground level, the wind hit them. They dropped the platform to the ground, where it shuddered and swayed momentarily, Jan recovered himself at once. Venus was beginning to affect on his back with outstretched arms and legs. He turned over cautiously and crawled back to his brain. It had been 500 years Sanchez. Oostpoort in the northern hemisphere of Venus, while Heemskerk He gestured for Jan to follow overturn. Shortly the two men returned with the fuel from the groundcar, its base was too low for it to had greeted Jan, gesturing. " asked Sanchez from the dome entrance. "I don't know," replied Jan. am Doctor Sanchez. We are very grateful you have come." "I thought for a while I removing his venushelmet. "This is Mrs. Murillo," said Sanchez. ," she greeted him. and spoke to Sanchez. asked Jan, astonished. She looked interpreted to Jan. "Is that drive back, and blastoff can't be delayed." Jan threw up his hands and went back into the dome. "I should have known that," he asked Sanchez. "There's nothing that can be done," answered Jan. "They may as well put the fuel back in my groundcar." Sanchez called orders to the of the Venus Shadow?" in Spanish and he nodded. She zipped him into a venusuit done," he repeated. "We can't make the trip overland because of the chasm out there in Den ," said Sanchez, shaking Jan's hand again. "Thanks," replied Jan. He donned if the trip over was any indication." Jan and Diego made their way back down the chain to the through, and waved farewell as Jan swung the groundcar around and headed back eastward. Jan was sorry. He had done his still shivering. Jan did not realize Vanderdecken when it blasted off for Earth, Jan did not know. But the boy was around eight he must realize the seriousness involved in a decision to send him all the way to Earth. Jan felt ashamed of the exuberant foolishness which had that amused him and his The chasm that had caused him such a long detour before planet together. He could not understand a word Diego said when liked Diego and wished desperately He turned to Sanchez.

<question>:
What was Jan referring to when he thanked Sanchez for the good luck wishes?

<options>:
A Dealing with the symptoms of Venus Shadow
B Helping the sick child
C The difficulty of the first crossing
D Returning to Earth

<answer>:

C