题目

George Gershwin，born in 1898，was one of America’s greatest composers．He published his first song when he was eighteen years old．During the next twenty years he wrote more than five hundred songs．Many of Gershwin’s songs were first written for musical plays performed in theatres in New York City．These plays were a popular form of entertainment in the 1920s and 1930s．Many of his songs have remained popular as ever．Over the years they have been sung and played in every possible way—from jazz to country．In the 1920s there was a debate in the United States about ja下列运算正确的是（ ）A．-22=4B．2-2=-4C．a•a2=a2D．a+2a=3a