A

Weather has a great influence(影响) on people．It influences people's health, intelligence (智力) and feelings．

In August, it is very hot and wet in the southern part of the United States．People there have heart disease and other kinds of health problems during this month． In the Northeast and Middle West, it is very hot at some times and very cold at other times．People in these places may have heart disease after the weather changes in February or March．

The weather can also influence intelligence． For example, in a 1982 study by scientists, the in scores of a group of students were very high during a storm, but after the storm their IQ scores were lower than usual level． So storms can increase intelligence．However, very hot weather can lower it． Students in the United States often do badly on exams in the hot months of the year．

Weather also has a strong influence on people's feelings．Winter may be a bad time for thin people．They usually feel cold during these months and they may feel unhappy during cold weather． In hot summer weather, on the other hand, fat people may feel unhappy． The sum- mer heat may make them tired and they are easy to get angry．

(     )21．lf thin people feel unhappy, the weather may be very _________．