题目

 Safety in schools has been of great concern because of frequent reports about accidents__ students got injured or killed while in school.   A. in which            B. for which       C. which             D. when 答案：A  设m、n是平面α内的两条不同直线，l1、l2是平面β内的两条相交直线，则α∥β的一个充分而不必要的条件是（　　） A、m∥β且 l1∥αB、m∥l1且 n∥l2C、m∥β且 n∥βD、m∥β且 n∥l2