题目

Rain is pouring down from the sky without any sign of stopping．Farmers begin to worry about their crops since it _____ as long as 24 hours．        A．would rain      B．had rained       C．was raining      D．has been raining 答案：D 解析: 略下列措施可以提高燃料燃烧效率的是(　　)     ①固体燃料粉碎　              ②液体燃料雾化　     ③煤经气化处理　              ④通入适当过量的空气 A．①③         B．①②③       C．①③④     D．全部