灭活疫苗的优点包括()。
A.接种次数少
B.无毒力回复之患
C.易于保存
D.可立即产生免疫力
E.既可产生体液免疫,也可产生粘膜表面免疫
参考答案:B, C
The computer was used in teaching. As a result, not only _____, but students became more interested in
the lessons.[ ]
A. saved was teachers' energy
B. was teachers' energy saved
C. teachers' energy was saved
D. was saved teachers' energy
某墙背垂直而且光滑的挡土墙,墙高6m,填土为无黏性土,其表观密度为γ=18kN/m3,=35°。
在7题的条件下,墙背上的主动土压力与总压力的变化情况为()。
A.墙背上的主动土压力不变,总压力增大
B.墙背上的主动土压力不变,总压力减小
C.墙背上的主动土压力减小,总压力增大
D.墙背上的主动土压力增大,总压力减小