重点讲解：
1. for no reason 无缘无故；莫名其妙；没有理由；
例句：For no reason at all the two men started to laugh.
两个人莫名其妙地开始大笑。
2. do one's utmost to do sth. 极度；极限；最大可能；
例句：He would have done his utmost to help her, of that she was certain.
他肯定会尽最大努力帮她，这一点她非常肯定。
3. prevent sb. from doing sth. 阻止；制止；阻碍；
例句：Only a serious mischance will prevent him from arriving tomorrow.
只有碰上极倒霉的意外变故,他明天才会来不了。
4. hush up 隐瞒；遮掩；不让…张扬；
例句：The crime was so base that everyone wanted to hush it up.
这一罪行如此卑鄙无耻，大家都不想声张出去。
5. knock on 敲；击；
例句：Please do not enter before knocking on the door.
进来前请先敲门。