Which one of the following functions is a surjection?
1
f : R → R given by f(x) = x3 + 2 for all x ∈ R
2
g : R → R given by g(x) = x2 + 2 for all x ∈ R
3
h : Z → Z given by h(x) = 3x + 2 for all x ∈ Z
4
ϕ : R → R given by f(x) = x2 - 3x + 2 for all x ∈ R