A geometric sequence is defined recursively by an = 4an-1 . The first term of the sequence is 0.5. Which of the following is the explicit formula for the nth term of the sequence?
A. 0.5 4n-1
B. 0.5 4n
C. 4 0.5n
D. 4 0.5n-1
E. 0.5 4n+1