人体发育始于（　　）

已知集合A={x|3≤x＜7}，B={x|x²﹣12x+20＜0}，C={x|x＜a}．

（1）求A∪B；（∁_RA）∩B；

（2）若A∩C≠∅，求a的取值范围．

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                                                                                                                                             木芙蓉
                                                                                                                                        南宋•吕本中
                                                                                                                    小池南畔木芙蓉，雨后霜前着意红。
                                                                                                                     犹胜无言旧桃李，一生开落任东风。

以下体现社会主义法制建设中“执法必严”的是(    )

已知∠α、∠β，求作∠AOB，使∠AOB=∠α﹣∠β．