B. inn
According to the passage they all came to the hostelry, so it needs to be a place. Therefore, group is incorrect. It would make sense that at "nightfall" travelers were looking for a place to stop for the night and take shelter. This also eliminates fountain. Also, looking at clues from the excerpt, there are 29 people who "chanced", or just happened by fate, to end up getting together to ride to Canterbury town. Since we are talking about people and not animals, we should also eliminate stable as an option. During this time period, many people traveling would stop at inns along their travels to take shelter during the night. They would often gather in the dining area on the first floor of the inn and talk about their adventures.