单项选择题
A.19kv B.19.5kv C.21.5kv D.22kv
A.1 B.2 C.3 D.4
A.1‰ B.1.5‰ C.2‰ D.3‰
A.4-6mm B.4-8mm C.6-8mm D.8-10mm
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