单项选择题
A．examples of successful young men B．how to build up one' s position in society C．joys and pains of old people D．what to do when one has problems in life
A．moves in a quick but steady way year after year B．sends out less and less heat and light with each passing year C．radiates the same amount of light every year D．might have a strong influence on the weather patterns
A．The sun shines constantly and gives out the same amount of energy every year. B．The cause of the sun' s fluctuations is its loss of energy with each passing year. C．It is sure that the energy sent out by the sun will drop when more sun spots appear. D．Fluctuations in weather patterns are the results of the pull of gravity.