单项选择题

Questions 17 to 20 are based on the following passage. At the end of the passage, you will be given 20 seconds to answer the questions.
Now, listen to the passage.

What is the main topic of the passage

A.To introduce a new type of card game.
B.To tell people how to win money in poker.
C.To compare card game with doing business.
D.To explain the origin of some expressions.