控制区对空气洁净度要求是
A. 大于10万级
B. 10万级
C. 大于1万级
D. 1万级
E. 100级
Why were Sam and Joe chosen
A. The boss wanted them to get more experience.
B. The boss trusted them more than anyone else.
C. They were the last people who wanted to go.
D. They were the only men who offered to go.
According to the passage, Vienna was once a center of ______.
A. traffic
B. trade and science
C. art and music
D. and
下列物质常用于防腐剂的是
A. 甘油
B. 吐温80
C. 丙二醇
D. 单糖浆
E. 苯甲酸
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