第二部分：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）
21. The government has taken some measures to solve the shortage of electricity, but it may be some time ______ the situation improves.
A. since B. when C. before D. unless
22.My MP4 has disappeared. Who _______ have taken it away?
A. could. B. should C. must D. might
