Questions 11 to 20 are based on the conversation you have just heard.

A．They reduce a person’ s appetite.
B．They make a person less persistent in face of trouble.
C．They make a person’ s nervous system weak.
D．They make a person more vulnerable to disease.

A．To give an example of natural shapes.
B．To describe early sculpture.
C．To illustrate their use as tool.
D．To demonstrate their role as decorative objects.