What is the area included between a circle and an inscribed square of side 'a' units?

A

$$a^2(2\pi - 1)$$ sq. units

B

$$\left(\frac{a^2}{2}\right)(\pi - 2)$$ sq. units

C

$$a^2(2 - \pi)$$ sq. units

D

$$2a^2(\pi - 2)$$ sq. units