This kind of software for English study _____ a lot of students who are weak in oral English. [ ]

A. leads to

B. appeals against

C. contributes to

D. appeals to

天然琥珀在饱和盐水中一般（）

A.上浮在水面

B.漂浮在水中

C.下沉在水底

D.三种情况都有可能