— I was a volunteer for the 2008 Olympic games.
— ______. What a great experience we had!
A:So I am
B:So I was
C:So was I
D:So am I
定义在(﹣∞,0)∪(0,+∞)上的函数f(x),如果对于任意给定的等比数列{an},{f(an)}仍是等比数列,则称f(x)为“保等比数列函数”.现有定义在(﹣∞,0)∪(0,+∞)上的如下函数:①f(x)=x2;②f(x)=2x;③f(x)=x;④f(x)=ln|x|.则其中是“保等比数列函数”的f(x)的序号为( )