Two equal circles intersect so that their centres, and the points at which they intersect form a square of side 1 cm. The area (in sq.cm) of the portion that is common to the circles is

A

$$\frac{\pi}{4}$$

B

$$\frac{\pi}{2} - 1$$

C

$$\frac{\pi}{5}$$

D

$$\surd2 - 1$$