问题补充:
-----How long do you think it will be man can finally solve the problem of cancer?
------Well.it depends.
A. when
B. until
C. after
D. before
答案:
A. when
B. until
C. after
(答案→)D. before
解析:考查连词。本题考查it will … before …还有多久才能……。句意:——你认为人类还要多久才能解决癌症问题?——嗯,那还得看情况。故D正确。