If re were no mountains or oceans and if winds circled earth with perfect regularity n amount of heat and length of farmer's growing season would progress uniformly from north to south. Instead, re are all kinds of unexpected differences in climate, as temperature maps of United States show. For instance, all along western coast, temperature changes little between winter and summer. In some places, average difference between July and January is as little as 10 degrees centigrade. The climate along norrn part of this coast is similar to that of England. But in north central part of country, summer and winter are worlds apart. There average difference between July and January is 36 degrees centigrade and more violent extremes are common. The coldest days of a typical January may be 4 degrees centigrade, and hottest July day may be 45 degrees. This is sort of climate that is also found in central Asia, far from moderating influence of oceans. In eastern part of United States, difference between summer and winter is also very distinct, but not nearly so extreme. Near southwestern corner of country, climate is mild and spring-like in winter, but In summer temperature may reach equatorial intensity. In Alaska, almost continues daylight in summer makes short growing season an intense one. The variations in temperature within United States have had a marked effect on country's economy and living standards.
Question:

The economy and living standards are affected by .................. in temperature in United States.