Four letter-clusters have been given out of which three are alike in some manner and one is different. Select the letter-cluster that is different. 

The logic followed here is as follows: From the left end, the place value of the 1st letter, when written in English alphabetical series and the place value of 2nd letter, when written in reverse English alphabetical series, is equal. Similar logic is followed for the 3rd letter and the 4th letter. Option a: DWHS (Place value of D = Reverse of Place value of W), (Place value of H = Reverse of Place value of S) Option b: NMCX (Place value of N = Reverse of Place value of M), (Place value of C = Reverse Place value of X) Option c: RIEV (Place value of R = Reverse of Place value of I), (Place value of E = Reverse of Place value of V) Option d: FVIR (Place value of F = Reverse of Place value of U), (Place value of I = Reverse of Place value of R)