Refer to Exercise 1.12. Now suppose r = 2 and c = 4, but observations for the first two levels of B occur only at the first level of A, and observations for the last two levels of B occur only at the second level of A. In the corresponding model, E(yijk) = ????0 + ????i + ????j(i), B is said to be nested within A. Specify a full-rank model matrix X, and indicate its rank.