If you have any problems during your study here,please do not _______ to call me for help

With the help of the government , a large number of people ---_______ after the flood in 1991.

I have not heard anything from him since his _______.

John _______ to be a polite man. But in fact he is veryrude.

When a spacecraft travels, one of the major problems is reentry into the Earth ’s _______.