We must do whatever we can to ______the river from being polluted any more.
___ smoking here will be fined.
_____ with a good education can apply for the job.
According to the rules, students must not _____ their books during examinations.
She may have missed the train, in _____ case she won't arrive for another hour.
He had a lot of friends, none of _____ could lend him any money.