用渗析器进行水处理有除()之外的如下三条优越性
A.出水质量好
B.无环境污染
C.操作方法简单
D.成本低
参考答案:D
Maria has to baby-sit. That’s______ she can't come with us.
A.why
B.ho
C.when
D.what
槽形截面梁受力如图所示,该梁的变形为下述中哪种变形?()
A.平面弯曲
B.斜弯曲
C.平面弯曲与扭转的组合
D.斜弯曲与扭转的组合