Let 0<r<1 and a>0. Consider the geometric progression with first term a and common ratio r. Which statement about the partial sums Sn (sum of first n terms) is always true?
a) Sn decreases with n and tends to 0.
b) Sn increases with n but never exceeds 1−ra.
c) Sn increases with n and eventually equals 1−ra for some finite n.
d) Sn increases without any upper bound.