The growth of population during the past few centuries is no proof that population will continue 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 mn to adjust to productivity. How many significant demographic changes ever occurred in the past one million years

A. One.
B. Two.
C. Three.
D. Non