7. Given the universal set: U={a,b,c,d,e,f,1,2,3,4,5,6,7,8,9} let A={a,b},B={a,c,2,4,6}, C={1,2,3,4} and D=. Evaluate each expression: a) AB b) the relation on AC in which the second element of the ordered pairs is larger than 3. c) ABC d) CDAB