Which geometric series converges to 2/3?
a) (2/3 + 4/9 + 8/27 + dots)
b) (1/3 + 2/9 + 4/27 + dots)
c) (2/9 + 4/27 + 8/81 + dots)
d) (4/9 + 8/27 + 16/81 + dots)