Respuesta :
A the conclusion, because you should introduce your topic in the beginning of the essay. The conclusion is not in the beginning of the essay.
The answer to your question would be that the place the topic sentence should never be is in the conclusion. That is, your answer would be option A.
The fact is that you should not introduce brand new information in the conclusion. The closing paragraph/s should contain a summary of the whole piece of writing and your final opinion regarding the thesis. Therefore, the topic sentence should be at the beginning in order to develop the idea and present evidence supporting your claim.