21. Every evening after dinner, if not from work, I will spend some time walking my dog. A. being tired B. tiring C. tired D. to be tired
【答案】C
【解析】考查省略句式。在if引导的条件状语从句中，从句中还原应为if am not tired from work，根据省略的原则，所以答案选C。
22．Most Americans would prefer to keep their problems themselves, and solve their problems ______ themselves.
A. to; by B. by; to C. for; to D. in; on
【答案】A
【解析】句意为：大多数美国人宁愿让他们对自己的问题并自己解决他们的问题。By oneself表示“单独地，独自地”的意思。
23．When he the door, he found his keys were nowhere.
A. would open B. opened C. had opened D. was to open
【答案】D
【解析】考查非谓语动词。动词不定时的用法。句意为：当他要打开门的时候,他发现他的钥匙不见了。动词不定时表示将要发生的动作。
