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

A．Because the shape of snow crystal(晶体) is still a mystery for experts.
B．Because the snowfall is a blessing for human beings.
C．Because experts have different ideas about the formation of snowflakes.
D．Because it is not easy to judge the time or place of snowfall.

A．The clothes are not cleaned.
B．He doesn’t intend to get the clothes.
C．The woman should not watch him.
D．The woman does not look good.