什么叫烷烃？

传染病流行的三个环节是      、         和                。

蘩漪的个性特点是（）

A.抑郁乖戾

B.美丽温柔

C.热情强悍

D.极端而尖锐

E.娴静雅致

简述水生植物对水因子的适应。

多点夹紧是由一个作用力，通过一定的机构将这个作用力分解到几个点上，对工件进行夹紧。( )

Jane was badly taken in when she paid $300 for that second-hand bicycle; it was not worth

A．that all much

B．all that much

C．much all that

D．that much all