Reading Comprehension. Read the text and choose the proper word:
Thunderstorms are rain clouds that produce thunder and lightning. They form when the air 1) close/near to the ground is warm and humid. When this warm air 2) lifts/raises, it becomes cooler, and the water vapor in the air condenses, forming a cloud. If the cloud is warmer than the surrounding cloudless air, then the cloud will continue to 3) raise/rise. The greater the temperature 4) difference/variety between the relatively warm cloud and its surrounding air, the more 5) strong/vigorous the thunderstorm will be. If the wind speed and wind direction change significantly with height, the thunderstorm can rotate. These rotating thunderstorms provide the circulation that, when concentrated in a small area, 6) result/return in a tornado.
Because thunderstorms 7) reject/require warm, moist air, they occur most frequently in the tropics. In temperature latitudes, they are more likely to occur during the hot summer than during the cooler seasons. 8) Across/Over land, thunderstorms occur most frequently in the afternoon and early evening because land surfaces heat up dramatically during the day and cool down at night. In contrast, thunderstorms at sea are equally likely to occur at all hours because large water surfaces 9) enable/maintain an even temperature throughout the day.
