单项选择题


Passage Two
Questions 30 to 32 are based on the passage you have just heard.

A．Grassland for animals.
B．A land covered with trees.
C．A steep slope of a hill.
D．A land with fertile soil.
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单项选择题
According to Paragraph 1, we can learn that ______.
A．scientists have made certain achievements in HIV vaccine
B．HIV vaccine has been proved successful ultimately
C．HIV vaccine has been proved useless
D．HIV has already been decoded and defeated
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