Let d be the distance of a point P from the centre O of a circle of radius r. How many distinct tangents can be drawn from P to the circle?
(a) 0 if d≤r; 2 if d>r
(b) 0 if d<r; 1 if d=r; 1 if d>r
(c) 0 if d<r; 1 if d=r; 2 if d>r
(d) 0 if d<r; 2 if d=r; 3 if d>r