It was in the Ming Dynasty __________ the Great Wall was rebuilt to keep out northern tribes _________ threatened the Chinese heartland. A.that; that B.that; where C.when; that D.when; when 答案:A某风景区集体门票的收费标准是:20人以内(含20人),每人25元,超过20人的,超过的部分每人10元,某班28名学生去该风景区时,为购门票共花了多少钱?