阅读下面短文，从A、B、C、D四个选项中选出最佳选项。
This is a picture of Mr. Li's family. The man in the middle is Mr. Li. The woman is Mrs. Li's wife. They have two sons. The child behind Mr. Li is Li Lei. He's thirteen. The boy in front of Mrs. Li is Li Ming. He is seven. Li Lei and Li Ming are in the same school, but not in the same grade. Li Lei is in Grade Two. Li Ming is in Grade One. They are good students.
“○”和“●”表示不同元素的原子，下图表示单质的是（ ）
代表碳原子， 
代表氢原子。已知同温同压下，气体的体积比等于气体的分子个数比，m表示质量，V表示体积。该物质在氧气中完全燃烧生成水和二氧化碳时，下列关系式正确的是（ ）