The fourth term of a geometric progression (GP) is 16, and the 17th term is 128. Find the first term and the common ratio.
a. First term (a) = 2, Common ratio (r) = 2
b. First term (a) = 4, Common ratio (r) = 2
c. First term (a) = 2, Common ratio (r) = 4
d. First term (a) = 4, Common ratio (r) = 4