A.>3.500 B.>2.814 C.=2.814 D. <2.814
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.從兩個拱腳、兩個L/4處分別向拱頂方向安裝