People are warned ________ in that city because there is some virus going around the city.

Waste paper mustn’t _______. We should keep our environment clean.

He hurried to the railway station out of breath, only _______ that the train leaving for Shanghai had been away for half an hour.

If better use is _____ your spare time, you’ll make greater progress in that. [ ]

Did you regret having left your well-paid job?— Why should I? I _______ as much, but I enjoy my present one more.[ ]