A、It helps protect the bone and protects us from diseases. B、It may protect the bone and cure some diseases. C、It helps build up

Today, I’m going to talk about the health problems related to sun-tan. Sun-tan 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 the 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 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. Common skin diseases 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 sun-tan. Different skins react differently to sunlight, and expert opinion should be sought, especially in the beginning. The UVB 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 outmost layer are tanned by the UVA 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. 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.
23 What is the sign of getting a natural tan?
24 Why is the Ozone layer so important?
25 What is the specific function of Vitamin D3?