please help! What is the function for the graph

When x = 0 the value of the function is 2 so its either A or B.
When x = 1, y = 8 so substituting these values in A we get:-
8 = 2 * 8^1 = 16 so
its Not A. Try B:-
8 = 2 *4^1 = 8 which fits
Answer is choice B