Sentence completion: Choose A, B, C or D to complete each sentence. Câu 601: This class,______is a prerequisite for microbiology, is so diff...

Sentence completion: Choose A, B, C or D to complete each sentence.

Câu 601:

This class,______is a prerequisite for microbiology, is so difficult that I would rather drop it.

1. that                   
2. when                           
3. where                           
4. which