【正确答案】 A

【答案解析】[听力原文] Today I'm going to talk about the health problems related to suntan. Suntan is preferred by lighter-skinned people, especially during the summer months. They like to give their skin a nice natural bronze color with the help of sun tanning. Getting a natural tan is a sign of being healthy and being attractive. No wonder many people rush off to the beach at the onset of summer with their tanning lotions and laze away on a towel for hours on end. The result is a healthy tanned skin which people like to flaunt all day long. People often believe that a perfectly tanned skin improves their personality and the texture of their skin. However, it is not advisable to be in direct sunlight for a long time. Excess exposure of the skin to sunlight can actually damage the skin and is the leading cause of skin cancer all around the world. Moreover, in countries like Australia, the atmosphere does not filter the sun rays completely as the ozone layer in the atmosphere is depleting quickly. The ozone layer is responsible for filtering the harmful ultra-violet or UV rays of the sun that can damage the skin beyond repair. So what does a tan mean? A tan refers to exposure of the skin to the rays of the sun for a considerable amount of time. The UV-B rays of the sun encourage the cells of the innermost layer of the skin to produce more melanin pigments which on their way to the outermost layer are tanned by the UV-A rays of the sun. As a result vitamin D3 is produced naturally under the sun. The vitamin helps protect the bone and also protects us from diseases like osteoporosis. The direct rays of the sun also make the immune system stronger against the invasion of germs and increase the body's overall physical powers. It has a positive effect on the functioning of the heart and improves blood circulation. Common skin diseases like acne and neurodermatitis can be treated with ultra-violet light. These are just some of the many positive effects that the sun offers in the form of its ultra-violet rays. You should take the advice of experts if you would like to go for a natural suntan. Different skins react differently to sunlight. An expert opinion should be sought, especially in the beginning. Do not overdo a suntan, as excess exposure to the sun's rays can prove to be harmful to your skin. Wear a suntan lotion when you go out in the open during summer. Do not sunbathe for more than once a day. Going to the beach or lying out in the sun once or twice a week is enough to maintain a good tan on the skin. Tanning in summer proves to be very beneficial as it prevents skin fatigue, prepares your skin for the long summer months ahead, builds a natural protection and produces a nice natural tan. What is the main topic of the speech?