___ is known to us all is ____ the sun is bigger than the earth.

A It; that    B What ; that   C What ; how    D That; that

In his book,he explains both ______ it means to be a scientist and ______ science works.

A.how; how                                                                       B.what; that

C.what; how                                                                     D.how; that

There’s a saying: “ Life is 10% ____happens to us and 90% ______we respond to it.

A. who; why     B. what; how   C. which; when   D. that; that

_____ worries me is _____ we’re going to pay for all this.

A. It, that         B. That, how  C. What, how    D. As, that

______ some teenagers don’t realize is _______ difficult life can be after they get addicted to drugs．

       A．What, how             B．That, how            C．What, what a   D．That, what