题目

阅读下面短文，掌握其大意，然后从36-55所给的四个选项（A、B、C、D）中，选出最佳选项。 There is a beautiful story about a child playing with a vase his mother had left on the table for a few moments. When the mother turned   16   the sound of her son’s crying she saw that his   17   was in the vase and was apparently stuck. She   18   to help him and pulled and pulled until the child cried out   19 . But the hand was stuck fast（牢固地）. How would they get it out? The father suggested   20   the vase but it was quite valuable and the （2013•黄埔区一模）如图所示，在棱长为2的正方体ABCD-A1B1C1D1中，E，F分别为线段DD1，BD的中点．（1）求异面直线EF与BC所成的角；（2）求三棱锥C-B1D1F的体积．