- Statement a: True, all polynomials are rational functions but not all rational functions are polynomials.
- Statement b: True, \( f \circ f \) is a quadratic polynomial.
- Statement c: False, the degrees of \( f \circ g \) and \( g \circ f \) are not necessarily equal.
- Statement d: False, \( g(x) = f(x+2) \) shifts the graph left.
\[
\boxed{\text{a: True, b: True, c: False, d: False}}
\]