Do you know why the river was polluted? — Many different factors ___________ the serious pollution of the river.

On weekends， I ______ watch TV ______ play computer games.

In order to find out how the famous painting was stolen as soon as possible, more experienced policemen have been sent to _____ the case.

If the university ________ such a good reputation, I would not have come here.

People develop _______ preference for a particular style of learning at _______ early age and these preferences affect learning.