涂改液用量少毒性却不小，大多数涂改液使用时会闻到特殊的气味，从分子的角度可以解释为（   ）

读“黄河水系图”，完成下列问题．

Nat lived in a small town in England. He always stayed in England for his vacation, but last year he thought, “I’m never outside this country. All my friends go to Spain , and they like it very much. So this year I’m going there, too.”
First he went to Madrid (马德里) and stayed in a small hotel for a few days. On the first morning he went out for a walk. In England people drive on the left, but in Spain they drive on the right. Nat forgot about this and when he was crossing a busy street, a bike knocked (撞) him down.
Nat lay (躺) on the ground for a few seconds and then he sat up and said,
“Where am I ?”
An old man was selling maps at the side of the street, and he at once came
to Nat and said, “Map of the city, sir ?”

下面的四幅图是我国的冬小麦、油菜、水稻和甜菜的集中产区分布图，图序与下列排序一 致的是