Express each of the following functions in disjunctive normal form* (DNF) in the smallest possible number of variables: (a) f(a, b, c, d) = (a'c'+c)(ab'c+d')+(cd'+b')(cd'+c)+ab'd'+a'bc'd (b) g(x, y, z, w)=(x+yz)'+(y'z+y'z')(x'y'z+w')+y, z'w + y'zw (c) h(x, y, z)=(x'+z)(x+y')(x'+z') * For a given function, a disjunctive normal form is the same as the sum of minterms