The sum of first 20 terms of the sequence \( 0.7,0.77,0.777, \ldots...

The sum of first 20 terms of the sequence \( 0.7,0.77,0.777, \ldots \), is
(2013 Main)
(a) \( \frac{7}{81}\left(179-10^{-20}\right) \)
(b) \( \frac{7}{9}\left(99-10^{-20}\right) \)
(c) \( \frac{7}{81}\left(179+10^{-20}\right) \)
(d) \( \frac{7}{9}\left(99+10^{-20}\right) \)