A.≤13m; B.≤16m; C.≤20m; D.>20m
A.10m; B.13m; C.16m; D.20m
A.方便施工人員勞動組合; B.適應(yīng)流水作業(yè)法; C.便于工人操作; D.使拱圈在砌筑過程中均勻受力、均勻變形