Question

—Susan stays alone in the classroom and looks sad.
—_____________to her?

1. A.
   What happens
2. B.
   What has happened
3. C.
   What is happening
4. D.
   What was happening

Answer 1

B
B “某人发生了某事”即sth. happen to sb.，happen一般不用于进行时；Susan不高兴，说明是（已经）发生了某事，故用完成时，且完成时表示不高兴的原因。