Headings and subheadings in a text are used to organize the text neatly, and to have the reader better understand what you are talking about.
I believe the answer is A. This is because the sentence is supposed to be parallel and all of the verbs(except for hiss) have to be past tense.
It relates to the actual meaning which is "<span>a substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change."</span>
Entertaining
At your aunt's retirement party, you would want to give a fun, entertaining speech incorportating a story about your aunt.
At a retirement party, you don't need to persuade anyone to do anything, since you knew about the retirement party, you would have planned a speech (so it would not be extemporanous and done spontasiously) and there's no need to inform anyone of anything at a retirement party.
Did he realize his mistake? - interrogative
He didn't realize his mistake. - Negative
