The group’s research has done much to      our knowledge of the HIV virus．

You’d better put a cloth over the salad to ______ the flies for the sake of health.

Many suggestions were _______ at the meeting to help college students get jobs after graduation.

 This medicine will                    him of his cough.

Most parents take strong views against computer games which children are addicted to and _______ the closing of all net bars for such games.