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单选题
当发动机在地面运转时，APU将被用作主引气源当引气活门电门处于自动位，如果：（）With engines running on the ground, the APU is used as the primary bleed source with the BLEED VALVES switch in AUTO, if:（）
A
隔离活门被关闭 the isolation valve is closed
B
压力调节和关断活门打开 the pressure regulating and shutoff valves are open
C
无防冰系统工作 no anti-icing systems are operating
D
引气源电门选到APU the BLEED SOURCE switch is selected to the APU
答案解析
正确答案：C
