第二部分：英语知识运用（共两节，满分45分）
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，选出可以填入空白处的最佳选项，并在答题卡上将该项涂黑。
21. They form a polar molecule, _____ is, _____ with a slightly positive end and a slightly negative end.
A. which; that B. it; one C. that; one D. one; that
22. A recent report found that women graduates are more likely than non-graduates ____ childless throughout their lives.
A. remained B. to be remained C. remain D. to remain
23. One day you’ll _____ this foolish behavior.
A. pay B. pay for C. pay back D. pay off
