发动机工作时，如发生抖动，排气管放炮.冒黑烟等现象.多半是混合气（）.
A.正常
B.过富油
C.过贫油
D.减速
参考答案：B
将下面句子中错误处的标号填入题前括号内，并在后面的横线上进行改正。
( ) 1. What about something eat?
A B C D
( ) 2. It's time to going and play games.
( ) 3. Let me to have a look.
( ) 4. All of the students is Young Pioneers.
( ) 5. What's he doing? He's listening the radio.
( ) 6. A man behind the tree is my mother's brother.
对于有明确潜伏期的感染，入院后多长时间内发生的感染为医院感染 （）
A.24h
B.36h
C.48h
D.72h
E.超过平均潜伏期后
