As a teacher, you should not _______ the students from asking questions in class.

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

When traveling alone in the mountains, you ’d better take a _______ with you in case you get lost.

It is not ---_______ for me to return all the books to the library now because I still need some of them for my research.

This morning in the class, our teacher lost his ______at last because he could not stand any more.

Several loudspeakers are _______ from the ceiling and we can hear the speaker very clearly.

Without a proper education, people could _______ all kinds of crimes.

I have not heard anything from him since his _______.

Both sugar and salt can ______in water.

Students with _______ problems may apply for student loans.