拱桥中的拱圈或拱肋是主要的受力构件,拱轴线可以是抛物线、圆弧线、悬链线等曲线,在竖向荷载作用下,拱圈或拱肋任意截面以承受()为主。
A.拉力
B.推力
C.压力
D.剪力
参考答案:C
We do have the most supportive parents and teachers, ________will make a difference to our study, unless all of us make every effort .
A.none of them
B.all of them
C.none of whom
D.all of whom
减毒活疫苗的优点包括()。
A.接种次数少
B.免疫效果好
C.免疫维持时间长
D.易于保存
E.接种者无禁忌征