monopoly
垄断权，专利权 

例句：
An inventor has a monopoly on his invention for a certain number of years.
发明者对他的发明享有若干年的专利权。

rain cats and dogs
倾盆大雨
 
例句：
It's raining cats and dogs, so we can't go out to play right now.
外面正下着倾盆大雨，所以现在我们不能出去玩儿。

I'm just having a look.
我只是随便看看。

对话：
A: Do you need any help, sir?
B: No, thanks. I'm just having a look.
　
A：您需要帮忙吗，先生？
B：不，谢谢。我只是随便看看。