The engineers in this lab spent several weeks _______ their plans for the new bicycle

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.

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

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

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

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

Both sugar and salt can ______in water.

I have not heard anything from him since his _______.

Students with _______ problems may apply for student loans.