阅读下列资料，回答有关问题．
如图是淡水生态系统中的一条食物链：图中的黑色圆点表示的是排入水体中的某些有毒物质，这些有毒物质在生物体内是难以分解、无法排出的．
黑色圆点的多少表示有毒物质量的多少．读图回答40﹣44题．
下列关于有机物的说法正确的是（ ）
2015年5月,腾讯公司马化腾来重庆作了“以‘互联网+’为驱动,推动经济社会创新发展”的演讲,引起了李凯同学的兴趣。于是,他收集了下面两幅图片,进行研究性学习,现请你参与!
Dear Zhang Peng,
I have a new school. It's big and beautiful. There are many trees and beautiful flowers in it. The school buildings are yellow and white. We have a music room, an art room, a computer room and a library. I'm in Classroom 1. It's on the first floor. It's next to the library. I like our playground very much. It's so big , we often play football there.
Welcome to my school!
Yours,
John
细胞膜与其完成各种生理功能极为重要的结构特点是( )
