The correct answer is: A. Sooner or later we must all accept our obligation to future generations.
A persuasive essay is an essay that aims to convince the reader of a certain point of view and its superiority over opposing points of view. In the sentence, "Sooner or later we must all accept our obligation to future generations", the author is summing up his argument and persuading the readers to accept their "...obligation to future generations". Option B, C and D are not conclusions to a persuasive essay because they either state personal opinions or contain subjective claims.
