The teacher explained a second time the students should have difficulty in doing the expe

问题补充：

The teacher explained a second time, the students should have difficulty in doing the experiment.

A. although

B. in case

C. so that

D. but

答案：

A. although

(答案→)B. in case

C. so that

D. but

解析：句意:老师又解释了一次，以防学生们在做实验时有困难。Although尽管；in case万一；so that以便；but但是。根据句意故选B。