The absolute value of a complex number is called the modulus. This represents the DISTANCE to the origin from the point on the imaginary + real plane.
the real horizontal distance is 4 and the imaginary vertical distance is also 4. So to figure out this just use the Pythagorean theorem.
4^2 + (4)^2 = c^2
16+16 = c^2
c^2 = 32
c = 4sqrt2 = 5.66 or option D.