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

Correct option is C

​$$\text{Given letter clusters:} \\\text{1. RT: The difference between R and T is } T - R = 2. \\[6pt]\text{2. XZ: The difference between X and Z is } Z - X = 2. \\[6pt]\text{3. EH: The difference between E and H is } H - E = 3. \\[6pt]\text{4. LN: The difference between L and N is } N - L = 2. \\[6pt]\text{Observation:} \\\text{The difference between the letters in } \text{RT, XZ, and LN is } 2. \\\text{However, in } \text{EH, the difference is } 3. \\[6pt]\text{Thus, the odd one out is } \boxed{\text{EH}}.$$​​