题目内容：

改写句子
在改写后的句子空格处填上适当的单词,使改写后的句子意思在含义上与原局相同.每空限填一词.
1/Many people think that it is possible to reduce pollution in this area.
Many people think ______ ______to reduce pollution in this area.
2/Your clothes need washing.
Your clothes need _____ _____ ______.
3/You shouldn't speak to others until you are spoken to.
You shouldn't speak to others until____ _____ .
4/The house which was completed last year fell down last week in a heavy storm.
The house ______last year fell down last week in a heavy storm.