题目内容：

It is important to protect yourself from harmful rays. But if you think a high-factor sunscreen keeps you safe from harmful rays, you may be wrong. Research in this week’s Nature shows that while factor 50 reduces the number of melanomas（黑瘤）and delays their occurrence, it can’t prevent them. Melanomas are the most aggressive skin cancers. You have a higher risk if you have red or blond hair, fair skin, blue or green eyes, or sunburn easily, or if a close relative has had one. Melanomas are more common if you have periodic intense exposure to the sun. Other skin cancers are increasingly likely with long-term exposure.

There is continuing debate as to how effective sunscreen is in reducing melanomas – the evidence is weaker than it is for preventing other types of skin cancer. A 2011 Australian study of 1,621 people found that people randomly selected to apply sunscreen daily had half the rate of melanomas of people who used cream as needed. A second study, comparing 1,167 people with melanomas to 1.101 who didn’t have the cancer, found that using sunscreen routinely, alongside other protection such as hats, long sleeves or staying in the shade, did give some protection. This study said other forms of sun protection – no sunscreen – seemed most beneficial. The study relied on people remembering what they had done over each decade of their lives, so it’s not entirely reliable. But it seems reasonable to think sunscreen gives people a false sense of security in the sun.

Many people also don’t use sunscreen properly applying insufficient amounts, failing to reapply after a couple of hours and staying in the sun too long. It is sunburn that is most worrying – recent research shows five episodes of sunburn in the teenage years increases the risk of all skin cancers.

The good news is that a combination of sunscreen and covering up can reduce melanoma rates, as shown by Australian figures from their slip-slop-slap campaign. So if there is a heat wave this summer, it would be best for us, too, to slip on a shirt, use sunscreen and slap on a hat.

1.What’s people’s common expectation of high-factor sunscreen?

A. It will protect them from sunburn.

B. It will keep their skin smooth ad fair.

C. It will work for people of any skin color.

D. It will delay the occurrence of skin cancer.

2.What can we learn from the second paragraph?

A. Sunscreen can prevent all kinds of skin cancers.

B. The studies are based on direct observation of the subjects.

C. The studies may help people select the most effective sunscreen.

D. Daily application of sunscreen helps reduce the incidence of melanomas.

3.What does the author suggest in order to reduce melanoma rates?

A. Staying in the shade whenever possible.

B. Using covering up instead of sunscreen.

C. Using both covering up and sunscreen.

D. Applying the right amount of sunscreen.

4.What is the best title for the text?

A. No Way to Stop Harmful Rays!

B. Does Sunscreen Prevent Skin Cancer?

C. Did You Use Sunscreen In the Right Way?

D. Skin Cancer-The Biggest Threat to Human Beings!