Which of the following replacements for /* missing code */ will correctly implement the Circle constructor?
I.
center = new Point();
radius = r;
II.
center = new Point(a, b);
radius = r;
III.
center = new Point();
center.x = a;
center.y = b;
radius = r;
A. III only
B. I, II, and III
C. II and III only
D. I only
II only