for which of the following function f is f^-1 a function

for which of the following function f is f^-1 a function
f(x)=x^2
f(x)=x^3
3.f(x)= I X I


A.1
B.2
C.只有1和2
D.只有2和3
E.1和2和3
主要是求翻译，题感觉好绕