It is widely known that burning coal for electricity is one of the main causes for global warming , but we can’t ignore the cars’ _____ to the greenhouse effect.

tothe world, the dance “Gangnam Style” has gained greart great popularity

The teacher agreed to the suggestion that the students _________ two weeks to prepare for the exam without coming to school.

Economy is booming, so it is hard for some of the firms to _____ enough labor , though their working conditions are rather good.

The disaster-stricken village was inaccessible _______ by helicopter, and the storm added to the rescuers’ difficulty