Answer:
Option B
Explanation:
A) f(x) =x This is a straight line passing through the origin with slope = 1.
C) This is f(x) = x^2 a parabola open up
D) f(x) = |X| is a straight line y=x for x>0 and y =-x for x<0
Hence the above 3 cannot be an exponential parent functions.
Consider option B
f(x) =

This is obviously an exponential function since the variable x appears in exponent.
Base is 2.
Thus we have option B is the right answer