(Click on the graph for a larger version.)

Note that the first area (with vertical, red shading) is 18 and the second (with oblique, black shading) is 6.

A. $\int_a^b f(x) dx =$

B. $\int_b^c f(x) dx =$

C. $\int_a^c f(x) dx =$

D. $\int_a^c |f(x)| dx =$