Look at number 18 from a student's point of view (one who is overly cautious about being tricked). An argument could be made that at (-4,0), the graph looks to be tangent to the x axis and at x < -4, the graph appears to increase slightly. That would disqualify the exponential choice and make an argument for the quadratic. Again, we all understand the answer is exponential but, look at it from the suspicious, honor's kid point of view. I just don't know why they had to make it so close to the x axis.