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

问题补充：

You have failed two tests.Youd better start working harder, you won 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：考查“祈使句＋and/or＋陈述句”。因为祈使句与后面的陈述句所表达的内容是对立的关系，故用or(否则)。