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. In Haikou, ______ car is getting to be _____ popular means of transportation.
A. the; a B. a; 不填 C. the; the D. a; the
22. —Why didn’t Sam attend the party yesterday evening?
—He ___ not have wanted to see me.
A. should B. might C. could D. would
23. The purse found on the playground matches the ____ by Mary, so it must be hers.
A. direction B. expression C. description D. instruction
24. Leave your key with a neighbor ________ you lock yourself out one day.
A. soon after B. even if C. ever since D. in case
