题目

如图示，三根长度均为L的细杆AB、AC、AD下端固定在A点．AC杆竖直．α＞β，杆的端点连接有光滑金属丝BC、CD．金属丝上套有光滑小环甲、乙．使小环甲、乙分别从C点沿金属丝CB、CD下滑到B和D点，下滑时间分别为t甲、t乙．下列正确的是（                                                            ）                                                                                                                           　   A． t甲＞t乙         B．  t甲＜t乙 C． t甲=t乙=  D． t甲=t乙=                                                                                                                                       答案：D

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