Which letter/vowel combinations are involved in the Sandhi of the word 'Vyarth'?

The word 'Vyarth' splits as $\text{Vi}+\text{Arth}$. Here, the vowel 'i' ($\text{इ}$) from 'Vi' and 'a' ($\text{अ}$) from 'Arth' combine to form 'ya' ($\text{य}$) according to Yan Sandhi rules ($\text{इ}+\text{अ}=\text{य}$). Therefore, option D is correct.