单项选择题


Questions 15 to 17 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.
According to the lecturer, why did Europeans often knock on wood

A.Superstitions generally flow from cultural beliefs.
B.Superstitions are rooted in European culture.
C.Superstitions are irrational.
D.Superstitions are generally a European feature.