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