题目

由C、O两种元素组成的气体中，C、O元素的质量比为3：5，则该气体的组成可能是A.CO2和CO B.CO2和O2 C.CO和O2 D.CO2和C 答案：【答案】AC【解析】由碳、氧两种元素组成的气体有CO、CO2和O2，其中CO、CO2中碳与氧的质量比分别是3：4和3：8，所以不可能是某一种物质，也不可能是二氧化碳与氧气的混合物，因为那会使碳氧的质量比小于3：5．，也就是混合物中必然是一个的比小于3：5而另一个大于3：5。A、CO、CO2中碳与氧的质量比 请认真阅读下面短文，并根据所读内容在文章后表格中的空格里填入最恰当的词。 注意：每空一词。 　　In a society such as the United states or Canada, which has many national, religious, and cultural differences, people highly value individualism－the differences among people．Teachers place a lot of importance on the qualities that make each student special．The educational systems in these countries show these values．Students do not memorize information．Instead, they work individually and find answers themselves．There is often discussion in the classroom．At an early age, students learn to form their own ideas and opinions． 　　In most Asian societies, by contrast, the people have the same language, history, and culture．Perhaps for this reason, the educational system in much of the Orient reflects society's belief in group goals and purposes rather than individualism．Children in China, Japan, and Korea often work together and help one another on assignments．In the classroom, the teaching methods are often very formal．The teacher lectures, and the students listen．There is not much discussion．Instead, the students recite rules or information that they have memorized． 　　There are advantages and disadvantages to both of these systems of education．For example, one advantage to the system in Japan is that students there learn much more math and science than American students learn by the end of high school．They also study more hours each day and more days each year than North Americans do．The system is difficult, but it prepares students for a society that values discipline and self-control．There is, however, a disadvantage．Memorization is an important learning method in Japanese schools, yet many students say that after an exam, they forget much of the information that they have memorized． 　　The advantage of the educational system in North American, on the other hand, is that students learn to think for themselves．The system prepares them for a society that values creative ideas．There is, however, a disadvantage．When students graduate from high school, they haven't memorized as many basic rules and facts as students in other countries have．