正常的汽车空调系统，其相对湿度应能控制在（）范围内.
A. 25-35%
B. 35-45%
C. 45-65%
D. 65-78%
When you are firing a pyrotechnic distress signal，it should be aimed at（）.
A. straight overhead
B. at the vessel whose attention you are trying to get
C. into the wind
D. about 60 degrees above the horizo
我国大多数吸收稳定系统的吸收塔的塔板数都在（）块左右。
A. 25
B. 30
C. 35
D. 40
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