XD-1型低频信号发生器其频率的调整，必须要在排除（）以后进行。
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加油时燃油进入任一个通气油箱，除了导致溢流浮子作动外，还导致（）
A. 所有加油活门和主活门关闭
B. 所有加油活门关闭
C. 主加油活门关闭
D. 下次飞行前要排放燃油
Which of the following statements is TRUE regarding automatic identification systems (AIS)? （）
AIS is a global tracking system that relies upon INMARSAT C service to communicate vessel position and other safety related information to similarly equipped vessels，aircraft and shore stations within the area
B. AIS is a short-range 3 cm X-band radar system that automatically sends a vessel's position and other safety related information to similarly equipped vessels，aircraft and shore stations within the area
C. AIS is a short-range VHF-FM system that automatically broadcasts a vessel's position and other safety related information frequently to similarly equipped vessels，aircraft and shore stations within the area
D. AIS is a one-way centrally managed system that requires the local VTS to send commands to instruct each vessel to broadcast position and other safety related information to similarly equipped vessels，aircraft and shore stations within the area
社会总产品是社会各个物质生产部门在一定时期（通常是一年）内生产的（）
A. 全部生产资料的总和
B. 全部消费资料的总和
C. 全部物质资料的总和
D. 全部剩余价值的总和
抽放泵输入管路中应设置（）。
A. 开停传感器
B. 风速传感器
C. 甲烷传感器
D. 馈电传感器
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