单项选择题

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.

What is the main idea of the talk()

A.How to have the bike stamped.
B.How to protect your bike.
C.How to buy good locks.
D.How to report your lost bike to the police.