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单选题
当起落架正在放下或收上时，主起落架门靠液压顺序打开。
A
The main gear doors are pneumatically sequenced to remain open while the gear is extending or retracting.
B
The main gear doors are hydraulically sequenced to remain open while the gear is extending or retracting.
C
The main gear doors are automatically sequenced to remain open while the gear is extending or retracting.
答案解析
正确答案：B
相关知识点：
起落架动作时主起落架门开法
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