The derivative of a function f that is defined and differentiable on the set of real numbers is given as
$$f ^ { \prime } ( x ) = \begin{cases} 1 , & \text{if } x \leq 1 \\ x , & \text{if } x > 1 \end{cases}$$
Given that $f ( 1 ) = 1$, what is the value of $f ( 0 ) + f ( 3 )$?\\
A) 2\\
B) 3\\
C) 4\\
D) 5\\
E) 6