单选题
The idea of rain making is almost as old as man, but it was not until 1946 that man succeeded in making rain. In ancient times, rainmakers claimed (声称) to be able to bring rain by many methods: dancing, singing, killing various kinds of living creatures (including humans), and blowing a stream of water into the air from a kind of pipe. More recently, some rainmakers claimed to make rain by shooting guns, causing explosions, or burning chemicals, the smoke of which was supposed to cause rain to fall. These rainmakers asked for as much as 1,000 dollars to make an inch of rain. One was so effective that he was almost hanged. He was believed to have caused a twenty-inch rain in southern California that flooded that land, killed several people, and did millions of dollars' worth of damage. Before 1946, rainmakers were either liars or honest people who happened to have' good luck. Scientific rain making was started in that year by Vincent J. Schaefer, a scientist at the laboratories of the General Electric Company in New York State. His success was the result of a lucky accident that changed years of failure into victory.
单选题
It has been about ______ years since man succeeded in making rain.