汽车排气管冒兰烟的主要原因是（）进入燃烧室被燃烧。
A.水
B.润滑油
C.空气
D.可燃物
参考答案：B
When I went to Liu Feng's home yesterday evening,he ____dinner. [ ]
A. was having
B. had
C.will have
D. has had
镇静催眠药中等剂量时（）.
A．催眠
B．镇静
C．幻觉
D．兴奋
E．中毒
