题目

Have you ever dreamed of visiting a planet in the Milk Way (银河系)？While the trip sounds exciting, it would take years and years to reach your destination. So in the future, bedtime for astronauts may be more than a few hours of regular shut-eye. They would have to sleep for years.European researchers are now conducting hibernation(冬眠) experiments. The study may help them understand whether humans could ever sleep through the years it would take for a spaceflight to distant planets. “If there was an effective technology, it could make deep-space travel a reality,” said Mark Ayre 梨、桃等果树的栽培通常用_____来繁育优良品种。 [     ]A．嫁接 B．种子 C．扦插 D．压条