—May I speak to Mr. Smith?
— ,please.I'll see if he is in.
A:Look out
B:Hold the line
C:Keep up
D:Come on
①f(x)=sin π2 x;②f(x)=2x2﹣1;③f(x)=|1﹣2x|
其中存在“可等域区间”的“可等域函数”为( )