作为遗传信息载体的染色体，它的组成成分是[ ]

A．基因和脂肪    

B．DNA和蛋白质  

C．蛋白质和糖类    

D．无机物和糖类

请根据下面提示，写一篇短文。词数不少于50。

You are discussing the following picture with your classmates. Now you are telling them how you understand the picture and what makes you think so.

提示词：电动扶梯 escalator