In the Cartesian coordinate plane, the graphs of functions $f$, $g$ and $h$ are shown below.
The areas of the shaded regions A1, A2 and A3 shown in the figure are 1, 3 and 9 square units, respectively.
Accordingly,
$$\int _ { a } ^ { c } ( h ( x ) - g ( x ) ) d x + \int _ { b } ^ { d } ( f ( x ) - h ( x ) ) d x$$
what is the value of the integral?
A) 5
B) 8
C) 12
D) 13
E) 17