题目

 [1]Although known as an extraordinarily successful businessman, Warren Buffet comes off as a pretty ordinary person. [2]Looking back on his childhood, one can see how serious he was about making money. Buffet used to go door-to-door and sell soda pop. Later, he also worked at his grandfather’s grocery store. At the ripe age of 11, Buffet bought his first stock(股票). When his family moved to Washington D.C., Buffet became a paperboy for The Washington Post. While still in school, he was making $175 a month, a full-time wage for many young men. [3]From the beginning, Buffet made h某人用300牛的水平力推重1200牛的小车在水平路面上匀速前进．若小车在30秒内前进20米．在这个过程中，人对小车做功的功率是A.200瓦B.400瓦C.600瓦D.800瓦