题目

如图所示，正四棱锥P－ABCD的底面积为3，体积为，E为侧棱PC的中点，则PA与BE所成的角为 （A）          （B）           （C）            （D） 答案： CThe reason ______ most Chinese have healthy white teeth is ______ they eat a healthy diet. A．why; thatB．why; becauseC．that; thatD．for; that