最近，科学家发明了一种制作防火涂料的新工艺．该涂料是用含有淀粉的植物性废料加工成的无色糊状物．发生火灾时，这种涂在房屋楼板表面的涂料就会转变成一种黑色物质，覆盖在楼板表面，起到防火的作用．转变成的黑色物质能防火的原因是（　　）

     Yoga is a kind of sport. It is very popular around the world now. Everyone, young and old can do yoga. It's good for both men and women.

 Why do people like yoga? There's a short answer and a long answer to that question. The short answer is that yoga makes you feel better. Practising, breathing exercises and thinking make you healthier in body, mind and spirit. For many people, that's enough of an answer, but there's more if you are interested.
     Yoga began in India about 5,000 years ago. At that time, people wanted to be free, healthy and live a long life, so this kind of exercise was born. The early yoga was part of a religion (宗教). It was usually taught one to one—one teacher with one student. Yoga is an Indian word that means “to join together”. There are three parts of yoga altogether: exercise, breathing and meditation (沉思). In the past, people paid more attention to the spirit. The idea be­hind the exercise was to join the mind, body and spirit as one. Yoga can give you peace, help you feel relaxed, and have fewer worries and illnesses.