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单选题
主电源失效时，可采用单独并独立的子系统提供照明。
A
To avoid primary instrument damage, the separate and independent subsystems are used to provide oxygen.
B
Separate and independent subsystems are used to provide illumination in case of primary electrical power failure.
C
The separate and independent subsystems are adopted to prevent engine failure.
答案解析
正确答案：B
