A、環(huán)狀以太網(wǎng) B、星狀以太網(wǎng) C、總線以太網(wǎng) D、網(wǎng)狀以太網(wǎng)
A.直流穩(wěn)壓 B.直流變壓 C.交流穩(wěn)壓
A.地面 B.井下 C.大氣