碧玉妆成一树高，万条垂下绿丝绦”中的绿丝绦是由植物的____发育而来的。

下列与我国地质灾害发生无关的因素是（    ）

    Anne and Sue are good f____. They have the s____ age. They are both twenty-two. They both like sports. Most important, they both like new dresses. They usually go s____ together at weekends. Now they are in a c____ shop. There are d____ kinds of beautiful dresses. Anne wants a red dress. But Sue thinks the pink o____ is better.

函数f（x）=x²﹣2x﹣3，定义数列{ x_n}如下：x₁=2，x_n+1是过两点P（4，5），Q_n（ x_n，f（x_n））的直线PQ_n与x轴交点的横坐标．

   Flags have existed for over 3,000 years. The earliest flags were wooden or metal poles with a carving. About 2,000 years ago pieces of fabric were added to some poles for decoration. Over the next 500 years the free-flying part of the flag became more important.