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 can we infer from the passage
A．Dogs have a natural instinct to return home. B．Seeing-dogs sometimes may not obey its master. C．Dogs are kept mostly as companions for old people. D．Guarding dogs always run fast.