问题 单项选择题

假如你在研究中发现一种新的单细胞生物并鉴定该生物的分类,则以下何种特性与你的鉴定有关()。 ①细胞核的有无②核糖体的有无 ③细胞壁的有无④膜上磷脂的有无

A.①③

B.②④

C.①④

D.②③

答案

参考答案:A

解析:

A。解析:细胞核的有无是区分真核生物和原核生物的最主要的标准,故①选;细胞生物均有核糖体,因此不能作为鉴定的标准,故②不选;由于动物细胞没有细胞壁,而其他绝大多数生物都具有细胞壁,所以根据细胞壁的有无可以判断该生物是否是动物,故③选;所有细胞都含有细胞膜,细胞膜的基本骨架都是磷脂双分子层,所以不能根据磷脂的有无判断,故④不选。因此答案选A。

阅读理解

阅读理解。

      For one week in April, millions of people chose not to watch TV for “TV Turnoff Week”. TV Turnoff

Week started in 1995 and is more popular every year. Many people discover that you can have a good time

with the TV off. If that sounds crazy to you, just have a look at some numbers:

     ―An American teenager spends 900 hours every year at school; the same teenager spends 1,023 hours

every year watching TV. That's 2 hours 49 minutes every day. 

     ―An average (平均) British person (not just teenagers) watches 3 hours 35 minutes every day.

     ―In the US, most TV has adverts. American children see 20,000 adverts every year. By age 65, an

American has seen two million ads!

     But some research from Britain says that may not be a problem. The London Business School watched

people carefully during TV adverts and they discovered that people don't watch a lot of the ads. The

researchers discovered that the most common activity during the adverts was talking to other people in the

room. Many other people started reading or doing housework or changed channels during adverts. They

only really watched them about 25 percent of the time.

1. During TV Turnoff Week, many people don't _____.

A. watch TV

B. change channels

C. watch adverts

D. do their school work

2. From the passage we can learn that _____.

A. American children see more adverts on TV than their parents

B. British people spend more than 3 hours a day in front of their TV

C. Researchers noticed that most people changed channels during ads

D. An American teenager spends more time at school than watching TV

3. The writer's purpose is _____.

A. to advise us to spend less time on TV

B. to tell us how to avoid watching adverts

C. to show us how many adverts American TV has

D. to ask us to turn off TV during TV Turnoff Week

单项选择题