वर्णमाला के प्रतिरूप (pattern) के आधार पर निम्नलिखित में से कौन सा अक्षर संयोजन अन्य से भिन्न है?

Choose the pair that is different from the other pairs based on a specific logic.

Based on alphabetical order, three of the following four letter-clusters are alike in a certain way and thus form a group. Which is the one that does not belong to that group? (Note: The odd man out is not based on the number of consonants/vowels or their position in the letter cluster)