The meeting had been on for half an hour Miss Yang turned up.A. whileB. AsC. UnlessD. be

问题补充：

The meeting had been on for half an hour Miss Yang turned up.

A. while

B. As

C. Unless

D. before

答案：

A. while

B. As

C. Unless

(答案→)D. before

解析：考查从句中连词的选择。此处有“在—之前”。