根据句意，用所给动词的适当形式填空。
We will have a picnic on May Day if it _______(not rain).
He ______ (wash) his car when I went to visit him yesterday.
We are all working hard ______(realize)the China’s Dream.
In the past few weeks, many special things _________(take) place in the world.
As we all know PM2.5 ________(cause) by air pollution in some parts of the country.