Answer:
I would say that it would be best to delay stating the main idea until after all the supporting details have been presented <em>when the topic of the essay will be new or unfamiliar to most readers.</em> <u>The correct answer would be the last one.</u>
Explanation:
I chose the last one because, this being the case, it would be a good choice for the author <u>to first present the subject</u> and explain its details that are totally new for the audience, and then, at the end, make the statement, like if it was a kind of conclusion of everything he explained.
This, for me, would only be possible if we, as authors, know that our audience is <u>not aware</u> of the facts of the subject, and we first need to make a kind of big introducion to make our points. If not, this wouldn't be possible because in a regular essay we put the statement first and then we discuss the details to support the statement; we don't keep our opinion to ourselves to create suspense in an essay, it is just not that kind of text. We need to be more formal in an essay.