Final answer:
The first baseman is the one covering first base when a slow roller is hit down the first base line between the pitcher and the first baseman who fields the ball.
Step-by-step explanation:
When a slow roller is hit down the first base line, the first baseman is usually the one to field the ball. In this scenario, the first baseman would be the one covering first base.
In baseball, each defensive position has a specific area of responsibility. The first baseman is responsible for covering first base, which means they are positioned near the base and ready to receive throws from other fielders. The other players mentioned in the options (pitcher, second baseman, and shortstop) have different defensive positions on the field and typically won't be covering first base in this situation.
Based on the information provided, the correct answer to the question is b) First baseman.