If a topic sentence doesn’t relate directly to the thesis statement, the topic sentence is a.) irrelevant and should be revised or deleted b.)essential c.) should explain why

The correct answer is A) IRRELEVANT AND SHOULD BE REVISED OR DELETED.
Topics sentences should support the thesis statement, so their relation with it should be clear and concise. Afterwards, each topic sentence can be further explained, exemplified or expanded. However, first of all topic sentences must summarize the main idea of the paragraph and show how it is related to the thesis statement.