单项选择题
A．stays the same throughout the year B．varies from day to day C．changes with the seasons D．changes from year to year
A．increases the ability to think B．is the best time for thinking C．is better for thinking than is very warm weather D．decreases the ability to think
A．a great effect on everyone's intelligence B．same effect on most persons' intelligence C．some effect on a few persons' intelligence D．no effect on most persons' intelligence