In a circle with centre O, AD is a diameter and AC is a chord. Point B is on AC such that OB = 7 cm and $$\angle OBA = 60^\circ$$. If $$\angle DOC = 60^\circ$$, then what is the length of BC?

A

$$3\sqrt{7}$$ cm

B

3.5 cm

C

7cm

D

$$5\sqrt{7}$$ cm