Every science, Aristotle points out, must begin with a few of these necessary ______ or general truths.

In this sentence, “or” sets up the contrast between the blank and general truths. “General truths” imply the truths by nature i.e. natural truths. Therefore, the blank must characterize the universal accepted truth. “Axiom” is an established principle or law of a science, art, etc. i.e. a proposition assumed to be true, hence it fits our prediction and is the answer. “Avowal” is an open acknowledgement or declaration, which is not contrary to general truth; hence ruled out. On the same lines, “comments” is also ruled out. “Promulgate” (to publish or make known officially - a decree, church dogma, etc) and “placard” (a notice for display in a public place; poster) implies advertisement in a broader perspective; therefore ruled out as they are off the track. Hence, (2) is the answer.