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

CK

 1   2    3    4   5    6   7     8    9  10  11  12  13

 A   B   C    D   E    F   G    H    I    J    K    L   M

 ↓    ↓    ↓    ↓    ↓     ↓   ↓    ↓     ↓   ↓    ↓    ↓    ↓

   Z   Y    X   W   V    U   T    S    R   Q   P    O   N

26  25  24  23  22  21  20  19  18  17  16  15  14

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FX ⇒ Position value of F (6) , Position value of X (24) (6 × 4 = 24)

DP ⇒ Position value of D (4) , Position value of P (16) (4 × 4 = 16)

ET ⇒ Position value of E (5) , Position value of T (20) (5 × 4 = 20)

CK ⇒ Position value of C (3) , Position value of K (11) (3 × 4 = 12) (ODD)