It will be another 50 years our country is expected to reach the level of a medium developed country.
A. since
B. before
C. that
D. when
网友回答
A. since
(答案→)B. before
C. that
D. when
解析：B 考察连词。句义：五十年以后我国才有望达到中等发达国家的水平。It is+一段时间+before从句，过多久…才…；遵循主讲从现的原则，B正确。Since引导时间状语从句，从句用一般现在时，主句使用现在完成时。故B正确。