Questions 11 to 13 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. The Northern industrialists were quick to take to tipping because ______.
A．they thought they were richer than the Southern slave owners B．they were winners in the Civil War C．they wanted to show off their fortune D．they wanted to learn from the Southerners