One possibility is the variable behavior of the sun．Astronomers at one research station have studied the hot spots and ‘cold’ spots (that is, the relatively less hot spots)on the sun．As the sun rotates(使旋转)，every 27．5 days，it presents hotter or colder faces to the earth，and different aspects to different parts of the earth．This seems to have a considerable effect on the distribution of the earth atmospheric pressure，and consequently on wind circulation．The sun is also changeable over a long term：its heat output goes up and down in cycles，the latest trend being downward．

　　‘

　　Scientists are now finding shared relations between models of solar weather interactions and the actual climate over many thousands of years，including the last ice Age．The problem is that the models are predicting that the world should be entering a new Ice Age and it is not．One way of solving this theoretical difficulty is to assume a delay of thousands of years while the solar effects overcome the inertia(惯性)of the earth‘s climate．If this is right, the warming effect of carbon dioxide might thus be serving as a useful opposed balance to the sun’s fading heat．

　　46．It can be concluded that a concentration of carbon dioxide in the atmosphere would

　　．

　　A．mean a warming-up in the Arctic

　　B．raise the temperature of the earth’s surface

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