单项选择题 （）可以提高我们的唤醒水平，使我们进入最优的工作表现

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.

Sometimes it is very difficult to （        ）some of the English words. Even the native speaker can not help.

Carelessness made him fall in his job （       ）.

Some states in the United States （        ）people to carry guns.

This boy was （        ）for what he had done in the class.

Some lazy men would rather （        ）than work.