钢背楞的容许挠度值为()A.L/400 (B.L/500 (C.L/600 (D.L/800 钢背楞的容许挠度值为()A、L/400 (B、L/500 (C、L/600 (D、L/800 发布时间:2025-07-10 20:27:53