Prove the following statements about a circle of centre O:
a. (i) No tangent can be drawn to the circle from a point lying strictly inside it.
b. (ii) Exactly one tangent can be drawn to the circle from a point lying on it.
c. (iii) Exactly two distinct tangents can be drawn to the circle from a point lying outside it.
d. Give clear geometrical reasons and, where necessary, supporting constructions for each part.