21．—Which of the twin brothers is easier to get on with?— yo

21．—Which of the twin brothers is easier to get on with?— younger one.He is most humorous
详细解析21．—Which of the twin brothers iseasier to get on with?
— younger one.He is most humorous man.
A．A; a B．A; the C．The; a D．The; /
22．—What do you usually do in summervacations?
—I usually travel around the country,but this year,I will do somevoluntary work a change.
A．with B．in C．toward D．for
23．Invention can be as it may suddenly begin just by noticingsomething usual.
A．accidental B．careless C．necessary D．imaginative

21 C the younger one ,这里the特指那个年轻的弟弟,a most humorous man,这里 most 不是最高级很容易写成 the most humorous man 表明他是最幽默的,此处的most意思为非常的；特别的 ,形容词,他是一个非常幽默的人.
22 D --你暑假通常做些什么?
—我通常四处旅游,但是今年我想做些志愿者工作改变一下.for a change 为了改变一下；为了换换口味
23 A 偶然的 B粗心的 C 必要的 D有想象力的
发明可能是偶然的,因为可能在注意到平常的事情瞬间就发生.