Let $$f(x) = 2x+1 \quad\hbox{and}\quad g(x) = x^2-1$$
Then
A. $(f \circ f) (x) =$ .
B. $(g \circ g) (x) =$ .
C. $(f \circ g) (x) =$ .
D. $(g \circ f) (x) =$ .