高中英语题解释一下，谢谢

7\I found cat ____ under the bed,who had caught a mouse.
A. hiding B.hidden
answer: B 这个我不知道
8\____this instrument should have put its work permit number on the box.反正看见这种，肯定选Whoever，因为有双重的指代作用
A.Whoever inspected B.No matter who examined
answer: A
9\They arrived there at last,____ .
A.being tired and hungry B.tired and hungry
answer: B 形容词作后置
10\We agreed to accept____ they thought was the best tourist guide.
A.whomever B.whoever
answer: B A选项那个词不存在
11\Terry doesn't like the idea of his wife ____in that affair.
A.being involved B.to be involved
answer: A 动名词作后置定语
12\____ I admit that there are still some problems about the traffic in
this area,I don't mean that it can't be solved.
A.Until B.As
answer: B 表示“当”
13\"____are the Olympic Games held?" "They ____ once every four years."
answer:How often, occur 用法？How often问频率的，occur表发生
14\Tom hopes to become a friend of ____ share his interests.
A.whoever B.whomever
answer: B 这个答案不对，B选项那个词不存在
15\I don't have a job.I would find one but I ____no time.
A.had had B.have
answer: B 现在没时间，如果有，就会找。所以前面用了虚拟语气
16\The prize winner stood on the platform,____. He could hardly keep

back his tesrs.
A.excited B.excitedly
answer: A 表示这个人是兴奋的，而不是动作兴奋
17\Will you buy me a stamp if you____ a post-office.
A.will pass B.are passing
answer: B 我个人觉得没太大差别
18\We often heard of people ____ in some countries.
A.being robbed and beaten up B.be robbed and beaten up
answer: A heard of someone doing something
19\It's ____so easy as you imagine.
A.not nearly B.hardly
answer: A 你确定你没拼错答案选项？
20\____ hearing the news,all of us jumoed with joy.
A.On B.By
answer: A 表示当
21\Naughty as my brother is, ____he is never late ____ his homework.
A.but...for B./...with
answer: B as引导从句，所以逗号后面是主句，不需要引导词了

7题我回答，这个是过去分词做定语，修饰CAT的，就像the baby crying的意思一样，互通的。