I think 3 sentences as a "quote" counts as "fair use".
Unlikely that three sentences is fair use if, for example, the entire page consists of six sentences. It's not the amount of content that is copied that constitutes fair use. It's closer to the percentage and how it is used. Creating an arbitrary standard of three sentences as constituting fair game could lead to problems.
Fair use is more along the lines of what percentage of the total (smaller is better) and how the content was used (criticism, etc.).