四行程发动机是由进气、压缩、作功、排气完成（）个工作循环的。
A、四
B、三
C、一
D、二
参考答案：C
— I don't think this TV set is of good quality. Can you replace it with a new one?
— _____. But I have to talk to my manager first. [ ]
A. I'm sorry
B. No way
C. No problem
D. That's a question
正常情况下胸部MRI不能显示的结构是（）
A.胸腺
B.皮肤
C.胸膜
D.气管
E.食管
