Which one of following Boolean expressions is not logically equivalent to all of

the rest ?

(a) wxy' + wz' + wxyz + wy'z

(b) w(x + y' + z')

(c) w + x + y' + z'

(d) wx + wy' + wz'

Is it choice c? If so how do I show that a is logically equivalent to b and d ?