用方框中所给单词的适当形式填空，使句子通顺、正确。每词仅用一次。

“如果说人生是一望无际的大海，那么挫折则是其中骤然翻起的浪花。”我们可以从中领悟到（    ）

在由CO₂和O₂组成的混合气体中，测知碳元素的质量分数为20％，则混合气体中CO₂和O₂的质量比为

阅读判断。根据短文内容，判断下列句子的正与误。

Long long ago, there was no paper in the world. People had to write characters(汉字) in bamboo slips or stones.Then there was a man named Cai Lun who was a Chinese man. He made people use all kinds of things to invent paper. From then on, people can use paper to write on. Paper is a great invention. We always remember the great inventor Cai Lun. Nowadays paper is very useful in our work, study and our life.It really means a lot to human beings