单项选择题
A.7d B.14d C.21d D.28d
A.6M B.4M C.2M D.1M
A.±1% B.±2% C.±3% D.±4%
A.1:2.22:4.37 B.1:2.34:4.47 C.1:2.22:4.47 D.1:2.34:4.37
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