如图，平行四边形ABCD的面积是16，对角线AC、BD相交于点O，点M₁、N₁、P₁分别为线段OD、DC、CO的中点，顺次连接M₁N₁、N₁ P₁、P₁M₁得到第一个△P₁M₁N₁，面积为S₁，分别取M₁N₁、N₁P₁、P₁M₁三边的中点P₂、M₂、N₂，得到第二个△P₂M₂N₂，面积记为S₂，如此继续下去得到第n个△P_nM_nN_n，面积记为S_n，则S_n﹣S_n﹣1=____．（用含n的代数式表示，n≥2，n为整数）

    Look at my family t____. I have a g____ and a grandmother. They are old. They live with us. I have three c____. One of them is my uncle's d____. The other two are my aunt's s____. They are all lovely. We often play t____. Look at that man. He is my f____. He is a teacher. He is h____ with his students every day. Here comes my mother. She is beautiful. I am beautiful, t____. I have got a b____ and nice family.

    How about yours?

阅读下面语段，按要求答题。

       岁月的山峦积淀着沧桑，生命的泉水涤荡着chéng澈，心灵的花草弥散着芳香。这梦一般的岁月纯净而美好。悠然行走在美丽的世界里，让自己跨越的姿势①（A．粗犷B．优雅）而蹁跹。优雅是生活的姿态。优雅的生活，就是在某个细雨霏霏的春日里，双手托腮，独坐窗边，聆听窗外细雨独奏的美妙乐声；优雅的生活，就是严热的夏季，静坐大树下，感受微风带来的丝丝凉意；优雅的生活就是在②（A．天高气爽B．狂风暴雨）的秋季，慢步原野，与落叶对话，和秋雨相伴；优雅的生活，就是在白雪皑皑的冬季，jū一捧雪花，握一份惬意。

A．防止药品污染    B．防止试管破裂   C．防止实验误差