A family of Microsoft word processing software products for creating web, email, and print documents.
Each of the sentences, or at least Sentence 4, would need to be in individual paragraphs (created by using Enter)
See the article "Formatting applied to one paragraph affects the entire document” at:
wordmvp.com/FAQs/Formatting/WholeDocumentReformatted.htm
That article is written for Word when running under Windows, but there is probably something similar in Word on a Mac, though it will almost certainly be in another location.