[单项选择] 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.
"One rotten apple spoils the barrel" means ______. A. rotten apples can bring disorder to people’s health B. it is hard to choose bad persons from good ones C. one bad person in a group can influence others D. Rotten apples should be quickly thrown away