The ratio of the sum of n terms of two arithmetic progressions is given by (2n + 3) : (5n - 7). Find the ratio of their nth terms.
a. (4n + 5) : (10n' + 2)
b. (4n + 1) : (10n' - 12)
c. (4n - 1) : (10n' + 8)
d. (4n - 5) : (10n' - 2)