A.從跨中向兩端,500mm B.從跨中向兩端,400mm C.從兩端向跨中,400mm D.從兩端向跨中,500mm
A.300mm B.150mm C.200mm D.450mm
A.45°~60° B.40°~60° C.30°~45° D.根據(jù)架體的縱、橫間距確定