单项选择题
A.2.0m B.2.5m C.3.0m D.3.5m
A.20mm B.30mm C.40mm D.50mm
A.10MΩ B.20MΩ C.30MΩ D.40MΩ
A.40mm³4mm B.40mm³6mm C.50mm³4mm D.50mm³6mm
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