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I think rather than simply saying that you'd want to be a senior associate, you should also touch on what aspects of the seniority appeal to you. Basically, what it is that you will enjoy doing once you get to that level.Also, I believe that showing your interest in a particular area might backfire because you'd still have to do the rest of the seats during your TC and maybe it will give them the impression that you'd hate those seats.
I think rather than simply saying that you'd want to be a senior associate, you should also touch on what aspects of the seniority appeal to you. Basically, what it is that you will enjoy doing once you get to that level.
Also, I believe that showing your interest in a particular area might backfire because you'd still have to do the rest of the seats during your TC and maybe it will give them the impression that you'd hate those seats.