jmc

The small circle has radius $1$, thus its area is $\pi$. The large circle has radius $2$, thus its area is $4\pi$. The area of the semicircle above $AC$ is then $2\pi$. The part that is not shaded are two small semicircles. Together, these form one small circle, hence their total area is $\pi$. This means that the area of the shaded part is $2\pi -\pi =\pi$. This is equal to the area of a small circle, hence the correct answer is $\boxed{1}$.