In Situation E, why is the bat not considered interference when it hits B4's batted ball?

The bat is not considered interference when it hits B4's batted ball because it is viewed as part of the playing field. In baseball and softball, anything that is in fair territory is generally considered to be part of the playing field, including equipment that is on the ground. If the bat is lying on the ground and a ball hits it after being hit by the batter, it is treated similarly to any other object on the field. Therefore, the ball remains in play, and there is no interference called because the bat's presence is not seen as a player act that affects the play.

While other options might address aspects of the situation, they do not focus on the core rule regarding what constitutes interference. The concept of whether the bat was thrown by the umpire, whether B4 dropped it, or whether the ball was dead does not change the fundamental ruling that the bat on the ground is a non-factor in terms of interference. Hence, considering the bat as part of the playing field is the reason it does not result in interference in this scenario.