题目

如图，在四边形ABDC中，∠BAC=90°，AB=2，AC=4，E、F分别是BD、CD的三等分点，连接AE、AF、EF.若四边形ABDC的面积为7，则△AEF的面积为        ． 答案：2 Which of the following sings means “You aren’t allowed to park your car here”? A                                  B                          C                             D