①危害社会秩序   ②败坏社会风气    ③是发家致富的捷径   ④导致违法犯罪

若角$600°$的终边上有一点(-4,a)，则a的值是（   ）.

依次填入下面文字横线处的语句，衔接最恰当的一组是（ ）
冬日的清晨，漫步在松花江边，你常常会沉醉在这神话般的冰雪世界里；             ，               ；                ，               。千姿百态的淞花，              ，令人感叹造化之功；千枝银柳万株雪松，                ，令人感慨天意之奇。
①流水潺缓    ②凝筑了一个透明清丽澄澈晶莹的佳境   ③雾气轻飘
④雪柳招摇    ⑤编织成一簇簇春花夏草秋果冬树       ⑥银枝素裹

如图所示，PQ为一固定水平放置的光滑细长杆，质量均为m的两小球A、B穿于其上，两球被穿于杆上的轻弹簧相连．在A、B两球上还系有长度为2L的轻线，在轻线中间系有质量不计的光滑定滑轮E，C、D球质量分别为m和2m，用轻绳连接并跨过定滑轮．用手水平托住D球并保持D球静止状态，此时轻弹簧长度也为L，已知劲度系数为K，（弹簧在弹性限度内，重力加速度为g）求：

阅读下面的短文，从每题所给的A、B、C三个选项中选出最佳答案。

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