You will hear a recording. Type the missing words in each blank.
Three basic ingredients are required for a (1) ………………………… to form: moisture, rising unstable air, and a (2)……………………. mechanism. The sun (3) ……………… the surface of the earth, which warms the air above it. If this warm surface air is (4) ……………………. to rise, it will continue to rise as long as it weighs less and stays warmer than air around it. As the air rises, it (5) …………………… heat from the surface of the earth to the upper levels of the atmosphere. The water vapor it contains begins to cool, releasing the heat, and it (6) ………………………. into a cloud. The cloud eventually grows upward into areas where the temperature is below (7) ………………… . Some of water vapor turns to ice and some of it turns into water droplets. Both have electrical charges. Ice particles usually have positive charges, and the rain droplets usually have negative charges. When the charges build up enough, they are (8) …………………… in a bolt of lightning, which causes the sound waves we hear as thunder.
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