题目

如图，有以下四个条件：①∠B+∠BCD=180°，②∠1=∠2，③∠3=∠4，④∠B=5，其中能判定AB∥CD的条件的个数有（　　）                                                                                                                                                           A．1                            B．2                            C．3                            D．4 答案：C【考点】平行线的判定．                                                                       【分析】根据平行线的判定定理求解，即可求得答案．                                   【解答】解：①∵∠B+∠BDC=180°，                                                      ∴AB∥CD；                                                                                       ②∵∠1=∠2，                                                                                    ∴AD∥BC；                                                                                       ③∵∠3=∠4，                                                                                    ∴AB∥CD；                                                                                       ④∵∠B=∠5，                                                                                   ∴AB∥CD；                                                                                       ∴能得到AB∥CD的条件是①③④．                                                        故选C．                                                                                             【点评】此题考查了平行线的判定．此题难度不大，注意掌握数形结合思想的应用，弄清截线与被截线．                    

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