题目

 You’d better carry a(n) ________ tyre in the back of your car in case it breaks down on the way. A. extra          B. free               C. convenient         D. spare 答案：D预防儿童手足口病的环境消毒液可用“84”消毒液，其主要成分是NaClO ，NaClO中氯元素的化合价为A.-1B.+1C.+3D.+5