In everyday usage "hot" means "having a lot of heat". Many people think that "cold" is something completely separated from heat. But this is not true. "Cold" simply means "having little heat". Your life depends on heat. In fact, every living thing depends on it. Without heat, every living thing would be frozen to death. All living things get their heat from the sun, which provides the conditions in which life is possible. Since before the dawn of history, man has been able to make his own heat. He has been able to release the sun’s heat that is trapped in things such as wood, coal, and oil. And he has been able to use this heat. Heat has made civilization possible. With heat, man could melt metals. As man learned to use metals and fuels, industries grew. As a result, engines were invented. These are machines that change heat energy into mechanical energy. Engine can do the work of many men. Without engines industrial civilization is impossible. Yet when the first engines were built in the 17th century, men were still wondering about the nature of heat. "What is it" they asked. Not until the early years of the 19th century did they find the right answer. He has been able to release the sun’s heat that is trapped in things such as wood, coal, and oil. From this sentence we know ______ .

A. man can get heat from things like wood, coal, and oil
B. man cannot get the heat directly from the sun
C. only wood, coal and oil have heat
D. all the sun’s heat is trapped in things