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.

Two hundred years ago, people used to ______.

A．work on the farm and stay in a beautiful place
B．work on the farm and stay in the same place for most of time
C．work on the farm and just stay in the same place for a very short period of time
D．work on the farm and often change the place where they lived