题目

There's ________interesting in the film, so ______is interested in it. A. something, nobody  B. nothing, somebody C. anything, anybody.  D. nothing, nobody. 答案：D 如图所示，在菱形ABCD中，∠DAB = 60°，PA⊥底面ABCD，PA = AB = 2，E、F分别是AB与PD的中点. (1) 求证：PC⊥BD； (2) 求证：AF∥平面PEC； (3) 求二面角P - EC - D的大小.