The following logic circuit represents the expression: X Y Y Z
(b) (X+Y) (Y+Z)
(c) (X.Y) (Y.Z)
((X+Y)’ + (Y+Z)’)’ = ((X+Y)’)’ . ((Y+Z)’)’ (Using DeMorgan’s first law)
= (X+Y).(Y+Z) (Using Inversion law)
So, the correct answer is (b).