The correct answer is A. Sources that reference only general baseball history and exclude semi-professional
Step-by-step explanation:
Most browsers, including academical ones, show results according to the words introduced and the connectors used to connect those words if there is any connector, due to this the words selected should be the keywords and the connectors or conjunctions used need to be appropriate as the results will vary according to those aspects. Considering this by searching for "Baseball AND history" the browser will include sources in which the two terms are included as the conjunction AND is a conjunction that connects words, additionally by adding NOT semi-professional, the browser will remove the sources that include the term semi-professional as Not indicates exclusion of something. In this way, the use of "Baseball AND history NOT semi-professional" will show results that include the words baseball and history, but not those including the term semi-professional.