The sun brings us light and warmth. But what can we do if the sun burns out？

　　There is no need to worry.

　　The sun is like a big stove using atom energy as its fuel. It bums¹ and bums， giving out tremendous² light and heat. Do you know how old the sun is？ It is over five billion years old. Yet it is still a "child"， not a"grandfather". The sun can live to dozens of billion years. Eventually the fire in this stove will go out， but before the sun dies out， people will have already found a way of replacing the sunlight and sun heat.