---How long do you think it will be China bees a developed country?
---At least 20 years, I guess.
A. that
B. until
C. when
D. before
网友回答
A. that
B. until
C. when
D. before
解析：it+段时间+before… 句型意为：要过多久才……。所在句意为：你认为中国要过多久才能成为一个发达国家。It …until…意为“直到……才……”与句意不合。