A.12m簡(jiǎn)支箱梁 B.22m簡(jiǎn)支箱梁 C.32m簡(jiǎn)支箱梁 D.42m簡(jiǎn)支箱梁
A.70% B.75% C.80% D.85%
A.2 B.3 C.4 D.5