用弹簧测力计竖直挂一铁球，当铁球露出水面$\frac{2}{3}$体积时，弹簧测力计示数为4N；当铁球浸入水中$\frac{1}{2}$体积时，弹簧测力计示数为1N，取下该铁球放入水中，铁球静止时受到的浮力是（　　）

请以“美丽的错误”为题写一篇不少于800字的记叙文。

纳米材料的出现对信息技术、材料技术的提高具有很大的推动作用。“纳米”实际上是一个长度单位，1纳米＝米。那么0.3纳米可能是下列哪个物体的长度 (    )

某生物的长尾对短尾为显性，控制基因为A﹣a，存在胚胎致死效应，假设有两种情况：甲情况为显性基因纯合致死；乙情况为隐性基因纯合致死．下列叙述不正确的是（　　）

阅读下列短文，从每小题所给的A、B、C、D四个选项中选出最佳选项。

     This week, I ask my students about fashion. I show each student seven things and ask their opinions(看法)about each thing. Some of their answers are interesting! Here is what the students in Class 8 like:

     Jodie Smith likes the key ring. Her friend Jordan says he can't stand (忍受)the scarf. “It's for old people!” He says. William Jones loves the wallet, and his classmate Gina Taylor loves the watch. Ann Rice doesn't like the watch, but she really likes the hair clip! Jerry Green likes the sunglasses. And the coolest thing is the belt! Everyone love it.