听力原文： Thunderstorms are the least dangerous and least violent of all the storms. Almost everyone has experienced a thunderstorm with its heavy rains, high winds, lightning and accompanying thunder. This type of storm can release a great deal of energy. A single thunderstorm can release energy to the atmosphere equivalent to a hydrogen bomb. There are some 50,000 thunderstorms that occur on earth daily. This would make the daily energy released into the atmosphere equal to billions of tons of TNT. Certain conditions must exist for thunderstorms to develop. First, the air must contain a great deal of water vapor. Second, there must be a rapidly rising air current. Thunderstorms may produce lightning and thunder. Lightning is a result of the rapidly rising air. The temperature produced by lightning is nearly 50,000 degrees Fahrenheit. This tremendous amount of heat causes the air to expand suddenly. This causes sound waves to be produced in the air which are heard as a crashing or loud noise called thunder. (34)