Describe the graphs that model the following problems.
(a) The multiplication of an n × n matrix by a vector of length n.
(b) The natural join of R(A, B) and S(B, C), where A, B, and C have domains of sizes a, b, and c, respectively.
(c) The grouping and aggregation on the relation R(A, B), where A is the grouping attribute and B is aggregated by the MAX operation. Assume A and B have domains of size a and b, respectively.