My friends went to summer camp _______ vacation. [ ]
A. at
B. on
C. in
D. for
答案:B
94×56.87+94×43.48+6×100.35.
总跨径是指多孔桥梁中各孔( )。
A.净跨径的总和 B.计算跨径的总和C.标准跨径的总和 D.经济跨径的总和