题目

 This is a picture of Dr. Yuan, a scientist ____ is well known in our country.   A. which       B. who           C. whom         D. whose 答案：B如图，在棱长为2的正方体中，为底面的中心，是的中点,那么异面直线与所成角的余弦值为                     A．　B．　 C．　　D．