A.10m; B.20m; C.25m; D.35m
A.從拱頂向兩拱腳安裝; B.從兩拱腳向拱頂安裝; C.從L/4處分別向拱頂、拱腳處安裝; D.從兩個(gè)拱腳、兩個(gè)L/4處分別向拱頂方向安裝
A.20°; B.30°; C.40°; D.50°