Ever since Ming furniture went on exhibit in Beijing, there       large crowds at the World Art Museum every day.

If the weather had been better, we could have gone outing. But it ____ all day.

Allen has decided that he will be an engineer by the time he ________ twenty.

(2013·高考江西卷)I________to visit you later that day，but I had to phone and cancel.

If  we ___________some measures, we might have prevented the environmental pollution.