ABCD passes through the centres of the three circles as shown in the figure. AB = 2 cm and CD = 1 cm. If the area of middle circle is the average of the areas of the other two circles, then what is the length (in cm) of BC?

A

$$(\surd6) - 1$$

B

$$(\surd6) + 1$$

C

$$(\surd6) - 3$$

D

$$(\surd6) + 3$$