单项选择题
A．all nature, including man, is growing then B．it lasts longer than the other seasons C．it is not too warm and not too cold D．both B and C
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