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.

How did the baker know customers came in

A.Customers would say "Hello" to him.
B.Customers usually bought fresh bread from him.
C.The managers always told him.
D.He could see customers from the balcony.