【单选题】

{{I}}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.{{/I}} Which of the following is a feature of the monastery cloister in the MiddleAges

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.