B. Answer the following questions. How did keeping silent help the teacher? Why did the boys take the vow of silence? For how long did the boys remain silent?

Without the specific story or passage, the exact reason the boys took a vow of silence cannot be known. However, common reasons for such a vow include taking it as a challenge to themselves, to practice self-discipline, or to reflect on the importance of quiet and listening, possibly inspired by the teacher's earlier actions.

$$\boxed{\text{To practice self-discipline, as a challenge, or for reflection, possibly inspired by the teacher.}}$$

The duration of the boys' silence is specific information that would be provided within the context of the story or passage. Without that specific text, it is not possible to determine how long they remained silent.

$$\boxed{\text{Cannot be determined without the specific story context.}}$$