阅读下面一首诗，完成下列各题。
                                                                                              饮酒 （其五）
                                                                                                                       陶渊明
                                                                                     结庐在人境，而无车马喧。
                                                                                     问君何能尔？心远地自偏。
                                                                                     采菊东篱下，悠然见南山。
                                                                                     山气日夕佳，飞鸟相与还。
                                                                                     此中有真意，欲辨已忘言。

如图，□ABCD中，EF∥AB，DE∶EA = 2∶3，EF = 4，则CD的长为（   ）