In this ques isn't only adenoidectomy

In this ques isn’t only adenoidectomy the ans since adenoids were the cause of impaired hearing so if they are removed hearing will improve on its own.

That we have to check by Otoscope or other examinations about the stage and progress of serous otitis media… I think the question is incomplete

There is already serous otitis media causing this condition; so to remove the fluid grommet insertion is necessary.

Here they didn’t mention anything which point towards serous otitis media. But you can take it this way. Adenoid → ET blockade → Serous Otitis Media. ET function will not be immediately restored after removing the adenoids. It will take time. Till then grommet will do the function of ET(that’s why it’s inserted in anteroinferior quadrant) and helps to drain the fluid accumulated in middle ear and also maintain middle ear pressure.

The question does mention “impaired hearing “.

With the given history, the most likely cause would be Serous otitis media.

Some for treatment, the complete answer should be option C.