用所给动词的适当形式填空（共10小题；每小题1分，满分10分）
The place was crowded. Mr. Brown didn't know where_______ (park) his car.
-The windows are dirty.
-I know. They_______ (not clean) for weeks.
We can never follow the fashion because it_______ (change) all the time.
Before John went to the USA, he_______ (be) a famous director in Hong Kong for many years.
In order to make the river clean, people should_______ (prevent) from throwing rubbish into it.
_______ (get) there on time, you need to get up early tomorrow morning.
I am very angry because I _______ (not receive) the things that I ordered online.
Nowadays people prefer_______ (shop) online to buying things in stores.
He told me that he_______ (return) my book before Sunday, but he didn't.
What a waste of time it is_______ (spend)so much time playing computer games!