第一节：单项填空（共15小题；每小题1分，满分15分）

从A、B、C、D四个选项中，选取出可以填写入空白的最佳选项，并在答题卡上将该项涂黑。
21．-Is____stronger of the two boys Peter?
-If you take____second  look,you will find it’s his twin brother Jim.
A.the;a  B.a;the  C.a;a  D.the;the
22.He made another wonderful discovery,____of importance to science.
     A.which I think is  B.which I think it is
     C.which I think it   D.I think is