So my justification, I haven't even looked at these choices yet, I would say for x is greater than three, f prime of x is less than zero. That would be my justification, not even looking at these choices. Now let's look at the choices. F prime is decreasing when x is greater than three. Now this isn't right. What we care about is whether f prime is positive or negative. If f prime is negative, if it's less than zero, then the function itself is decreasing.