The growth of population during the past few centuries is no proof that population will co

ntinue to grow straight upward toward infinity and doom. On the contrary, demographic history offers evidence that population growth has not been at all constant. According to paleo-ecologist Edward Deevey, the past million years show three momentous changes. The first, a rapid increase in population around one million B.C., followed the innovations of tool-making and tool-using. But when the new power from the use of tools had been exploited, the rate of world population growth fell and became almost stable.

The next rapid jump in population started perhaps 10,000 years ago, when men began to keep herds, plow and plant the earth. Once again when initial productivity gains had been absorbed, the rate of population growth abated.

These two episodes suggest that the third great change, the present rapid growth, which began in the West between 250 and 350 years ago, may also slow down when, or if technology begins to yield fewer innovations. Of course, the current knowledge revolution may continue without foreseeable end. Either way contrary to popular belief in constant geometric growth-population can be expected in the long run to adjust to productivity. And when one takes this view, population growth is seen to represent economic progress and human triumph rather than social failure.

Which of the following is net true according to the passage？

A．Human population expands at an exponential rate.

B．Population growth has shown fluctuation in demographic history.

C．Population growth can not be regarded as a social failure.

D．Increase in population is related to productivity.