A.面迎列車(chē) B.觀察列車(chē)運(yùn)行 C.目送列車(chē) D.觀察線(xiàn)路狀態(tài)
A.20m B.50m C.100m D.150m
A.三長(zhǎng)一短聲 B.兩長(zhǎng)一短聲 C.一長(zhǎng)一短聲