Determine which relation is a function.
a. number graph ranging from negative four to four on the x and y axes. a vertical line is drawn at x equals three.
b. number graph ranging from negative four to four on the x and y axes. a parabola is drawn with a vertex at (zero, zero) and extending off to the right. c. number graph ranging from negative four to four on the x and y axes. a circle is drawn with the point (two, one) on the perimeter of the circle.
d. number graph ranging from negative four to four on the x and y axes. an absolute value function is drawn with a minimum at (zero, zero).