A batter can reach first base through several means. Here are the ways from your list:
- Fly ball caught - Not a way to reach first base. If a fly ball is caught, the batter is out.
- Base hit - Yes, this is a legitimate way for a batter to reach first base.
- Error - Yes, if a fielder makes an error allowing the batter to safely reach first base, it counts.
- Walk - Yes, a batter can reach first base by receiving a base on balls (walk).
So, the correct ways from your list for a batter to reach first base are Base hit, Error, and Walk.