31. We should think of ways to stop the waste from the factory _____ our living environment. 

People exposed to radiation are more _______ to suffer from certain forms of cancer, which can be ______ but can’t be ______at present. 

Try to _____ the children down. They’re too excited.

The real cause of the problem ________ the poor construction of the bridge.

— What’s up?— There are so many problems ______.