Questions 19 to 21 are based on the conversation you have just heard.

A) It was the largest city of Alaska. C) There were a lot of wild animals around it.
B) It was a city of 40,000 people. D) There was no sign of human presence around it.-

A．People who sleep less than 8 hours a day are more prone to illness.
B．Poor sleep quality may be a sign of physical disorder.
C．Stroke is often associated with sleep.
D．Too much sleep can be as harmful as lack of deep.