Four letter-clusters have been given, out of which three are alike in some manner and one is different. Select the one that is different. (Note: The odd one out is not based on the number of consonants/vowels or their position in the letter cluster.)

In PTV: P(16), T(20), V(22) — differences are +4, +2. In LQO: L(12), Q(17), O(15) — differences +5, −2. In EJH: E(5), J(10), H(8) — +5, −2. In XCA: X(24), C(3), A(1) — +5(circular: 24+5=29→3 mod 26), −2. XCA follows the same pattern. Let me reconsider: PTV has gaps of 4 and 2 which is different from the +5, −2 pattern of the others. So PTV is the odd one out — but that's option (a). The answer is (a) PTV.