单项选择题
A.6860N/cm2 B.8820N/cm2 C.12270N/cm2 D.13720N/cm2
A.6000h B.6500h C.7300h D.7700h
A.4000～8000A B.≤4000A C.≤2000A D.≤1000A
A.1.73 B.1.92 C.2.25 D.2.5
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