问题 单项选择题

在维持细胞内液与外液渗透压平衡中,起决定性作用的是______

A.K+和Mg2+
B.Na+和Mg2+
C.K+和Cl-
D.Na+和Cl-
E.K+和Na+

答案

参考答案:C

解析:本题主要考查的知识点是体液的电解质组成与特点。
由于K+和Na+是细胞内、外液中的主要阳离子,不能自由透过细胞膜,而阴离子必须与阳离子配对同时存在,因此K+和Na+在维持细胞内液与外液渗透压平衡中,起着决定性的作用。

阅读理解

In the mid 1990’s, people started doing business on the Internet. At that time, there were two kinds of companies. First, there were traditional companies. They sold things in stores. Then there were Internet companies. They didn’t have a store, and they only sold things on the Net.

Traditional companies didn’t want to lose any business. Quickly they made their own websites and began selling things on the Net. These are the so-called “brick and click” companies. Many stores are made of brick. And you click on your mouse to buy things with your computer. That’s where the name “brick and click” comes from.

By the late 1990’s, e-business like amazon com , buy com. and etoys com. were in trouble. Their profits(利润) were not very high. Competition was great. Many of these businesses were losing lots of money. In 2000, many e-business went out of business.

Why are “brick and click” companies, like Barnes and Noble, Toys RVs and Walmart so successful? First, many customers know and trust their names. Their websites like walmart.com. are easy to remember. These companies also have lots of experience. They know how to run a successful business.

In the world of e-commerce, companies are fighting for every dollar and every customer. Will “brick and click” companies win the war? Only time will tell.

小题1:What did many traditional companies do in the mid 1990’s?                .

A.They went out of business.

B.They made their websites.

C.They bought Internet companies.

D.They sold their companies.小题2:What gave Internet companies lots of trouble in the late 1990’s?

A.Heavy competition

B.They were short of money.

C.They didn’t know what to do.

D.people didn’t believe in them.小题3:Which of the following is TRUE according to the passage?

A.All the “brick and click” companies run a successful business.

B.“Brick and click” companies are certain to win the business competition.

C.It is uncertain whether “brick and click” companies will win the competition.

D.Both “brick and click” companies and Internet companies will be successful in the future.

单项选择题