题目

阅读下列短文，从每题所给的四个选项 （A 、B 、C 和 D ）中，选出最佳选项。 The human brain contains 10 thousand million cells and each of these may have a thousand connections. Such enormous numbers used to discourage us and cause us to dismiss the possibility of making a machine with human-like ability, but now that we have grown used to moving forward at such a pace we can be less sure. Quite soon, in only 10 or 20 years perhaps, we will be able to assemble a machine as complex as the human brain, and if we can we will. It may then take us a long time to render 如图所示，取正方形纸片ABCD，将其沿对角线AC折叠，使B点落在D上，然后再折叠，使D点不动，B点落在AC上，设折痕交CD于E，请问：这时线段AD、DE与AC的长度有何关系?证明你的结论．