You have failed two tests. You’d better start working harder you won’t pass the course.

问题补充：

You have failed two tests. You’d better start working harder, you won’t pass the course.

A. and

B. so

C. but

D. or

答案：

A. and

B. so

C. but

(答案→)D. or

解析：

试题分析: 句意：——你已经两次考试不及格了。你最好现在开始努力，否则你这会挂科的。A并且；B所以；C但是；D否则。从句意可知此处指如果不努力将出现的结果，是对对方的警告，故答案选D。