问题 单项选择题

组成DNA和RNA的核苷酸.五碳糖和碱基各共有()

A.8.8.8种

B.8.2.5种

C.2.2.4种

D.2.2.8种

答案

参考答案:B

解析:试题分析:组成DNA的基本单位是脱氧核苷酸,有四种,组成RNA的基本单位是核糖核苷酸,有4中;组成DNA的糖是脱氧核糖,组成RNA的糖是核糖;组成DNA的碱基有A、T、G、C,组成RNA的碱基有A、U、G、C,故B正确。考点:本题主要考查核酸的结构,意在考查考生能理解所学知识的要点,把握知识间的内在联系的能力。

单项选择题

Most people would be (1) by the high quality of medicine (2) to most Americans. There is a lot of specialization, a great deal of (3) to the individual, a (4) amount of advanced technical equipment, and (5) effort not to make mistakes because of the financial risk which doctors and hospitals must (6) in the courts if they (7) things badly.

But the Americans are in a mess. The problem is the way in (8) health care is organized and (9) . (10) to pubic belief it is not just a free competition system. The private system has been joined a large public system, because private care was simply not (11) the less fortunate and the elderly.

But even with this huge public part of the system, (12) this year will eat up 84.5 billion dollars—more than 10 percent of the U. S. Budget—large number of Americans are left (13) . These include about half the 11 million unemployed and those who fail to meet the strict limits (14) income fixed by a government trying to make savings where it can.

The basic problem, however, is that there is no central control (15) the health system. There is no (16) to what doctors and hospitals charge for their services, other than what the public is able to pay. The number of doctors has shot up and prices have climbed. When faced with toothache, a sick child, or a heart attack, all the unfortunate persons concerned can do is (17) up. Two thirds of the population (18) covered by medical insurance. Doctors charge as much as they want (19) that the insurance company will pay the bill.

The rising cost of medicine in the U. S. A. is among the most worrying problems facing the country. In 1981 the country’s health bill climbed 15.9 percent--about twice as fast as prices (20) general.

15()

A.over

B.on

C.under

D.behind

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