飞机在地面，外流活门的工作是由其内部的哪个部件控制的？
A. 真空电磁阀（VACUUM SOLENOID）
B. 步进马达
C. 放泄电磁阀（DUMP SOLENOID）
户外试验应在良好天气情况下进行，且空气相对湿度不能高于（）%
Which statement(s) is/are TRUE concerning crane cargo operations? （）
A. Do not exceed rated load capacity of crane and container spreader or slings
B. During any cargo handling operation，the safety of personnel is paramount
Cargo handlers must be outfitted with adequate protection from personal injury
D. All the above
Constant superheat is maintained at the evaporator outlet of a refrigeration coil by a（）
A. solenoid valve
B. low pressure cutout switch
C. king valve
D. thermal expansion valve
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