Answer: the answer would be the thesis statement, as it is a statement which summarizes the main idea of the essay as a whole.
Explanation: the topic sentence is the sentence which describes the main idea of the paragraph, not the essay. the source citation is where you cite your sources if you have any, and the research question is the question you are asking yourself to help with your researching.
They talk to each other because they are separated by a brick wall which has a small crack in it. But the crack is big enough for them to whisper through
