Questions 18 to 20 are based on the following passage. At the end of the passage, you will be given 15 seconds to answer the questions.
Now listen to the passage. Which of the following is a feature of the monastery cloister in the Middle Ages
A．It was surrounded by a river. B．It generally had a fountain or a well at the center. C．It was surrounded by flowers. D．It generally had a wall at the center.