问题 问答题 简答题

伟晶矿床的物质成分特点:

答案

参考答案:

一杂(化学元素种类多,矿物共生组合复杂),二浓(40多种元素高度浓集,本身的克拉克值低);种类齐全,稀有宝库(各个大类的矿物在伟晶岩中都找得到,稀有元素在伟晶岩中也找得到);继承母岩,阶段演化(矿物成分与母岩具有一致性,演化上具有继承性,具有早期成岩晚期成矿的特点)。

阅读理解

阅读理解。

     A new study has found no evidence that sunscreen, commonly used to reduce the risk of skin cancer,

actually increases the risk.

     Researchers from the University of lows based their findings on a review of 18 earlier studies that looked

at the association between sunscreen use and melanoma (黑素瘤). They said that they found flaws in studies

that had reported associations between sunscreen use and higher risk of melanoma.

     Most health experts believe that by protecting the skin from the harmful effects of the sun, sunscreen

helps prevent skin cancer, which is increasing in incidence (发生率) faster than any other cancer in the

United States.

     But questions have been raised about sunscreen and whether it may have the opposite effect, perhaps

by allowing people to remain exposed to the sun longer without burning.

     The researchers said that among the problems with some earlier studies is that they often failed to take

into account that those people most at risk for skin cancer-people with fair skin and freckles (雀斑), for

example-are more likely to use sunscreen. As a result, it may appear that sunscreen users get cancer more

often.

     The studies, which generally relied on volunteers to recall their sunscreen use, were also unable to prove

how well the products had been applied, said the new study.

1. The underlined word "flaws" in the 2nd paragraph most probably means _____.

A. evidences

B. facts

C. faults

D. failures

2. People with fair skin and freckles _____.

A. seldom use sunscreen

B. are more in danger of skin cancer

C. can be free from the harm of the sun

D. often expose themselves to the sun

3. We can learn from the passage that _____.

A. sunscreen users get skin cancer more often

B. the volunteers have proved the effect of sunscreen

C. the new study was based on the experiences of volunteers

D. the number of skin cancer patients is increasing in America

4. Which of the following can be the beat title for this passage?

A. Sunscreen to Prevent Skin Cancer

B. Sunscreen to Increase Skin Cancer

C. Skin Cancer Caused by Sunscreen

D. Skin Cancer Caused by Freckles

单项选择题