—How long do you think it will be_______China sends a manned spaceship to the moon?
—Perhaps two or three years.
A.when B.until C.that D.before
—How long do you think it will be_______China sends a manned spaceship to the moon?
—Perhaps two or three years.
A.when B.until C.that D.before
D
before常用于以瞬间动词为谓语的肯定句和以持续动词为谓语的否定句中，表示“在……之前”。根据所提供的情景“Perhaps two or three years.”可判断出中国向月球发射载人人造卫星可能要两年或三年的时间。when表示“在……的时候”。until用于肯定句表示动作一直持续到until从句中的动作开始。