Lines AB and CD intersect at point O.
a. (i) Define (a) a linear pair of angles and (b) supplementary angles.
b. (ii) List all the linear pairs formed at the point of intersection O of the two lines.
c. (iii) Explain, without performing any numerical calculation, why the sum of the measures of each pair listed in part (ii) is 180∘. Your explanation should explicitly refer to the definition stated in part (i).