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单选题
发动机引气通常是：Engine bleed air is normally:
A
仅由10级压缩机提供。Supplied by the 10th compressor stage only.
B
仅由6级压缩机提供。Supplied by the 6th compressor stage only.
C
由10级压缩机提供，6级按需作为备用。Supplied by the 10th compressor stage, backed up by 6th stage on demand.
D
由6级压缩机提供，10级按需作为备用。Supplied by the 6th compressor stage, backed up by the 10th stage on demand.
答案解析
正确答案：D
