A.適當?shù)臏囟?br /> B.適當?shù)臐穸?br /> C.適當?shù)那鍧嵍?br /> D.以上條件都包括
A.20m B.30m C.40m D.50m
A.大于1歐姆 B.等于1歐姆 C.小于等于1歐姆 D.小于1歐姆