从每题所给的A、B、C、D四个选项中，选出可以填入空白处的最佳选项，并在答题卡上将该选项涂黑。
21. The most important thing to keep in ______ mind when dealing with______ emergency is to stay calm.
A. /; the B. the; an C. the; the D. /; an
22. — Honey, this is a present for your birthday.
— Ah! A pair of shoes, a well-known brand — Nike! I think it must ______ comfortably.
A. be worn B. be wearing C. have worn D. wear
