Manypeoplehaveheardofthe“braindrain”.Thisis

问题详情：

Many people have heard of the “brain drain”. This is ________ happens ________ people with good skills and a good education move to other countries for study or work, often at great expense to their home countries.

A. which; when  B. what; that  C. what; when  D. why; when

【回答】

C

知识点：连词

题型：选择题