单项选择题

Questions 29 to 32 are based on the passage you have just heard.

A．Their tasty meat.
B．The principle of their defense system against disease.
C．Their solid skin.
D．The principle of their birth modes.

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单项选择题

单项选择题

Questions 29 to 32 are based on the passage you have just heard. 您的浏览器不支持 audio 元素。