单项选择题

Dolphins once were hunted for money because______.

A．they are rare and precious animals
B．valuable oil can be obtained form their head
C．they can produce oil for lubrication
D．they are able to utter sounds worth study

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单项选择题

Which of the following is true according to the passage

A．5 million dolphins were hunted commercially from 1959 to 1972.
B．People's recognition of animal rights helps protect dolphins.
C．Dolphins am good at giving out sounds.
D．Clicks are used by dolphins to influence other dolphins' behaviour.

单项选择题

Which of the following is NOT true about Sasser and Netsky

A．They were created by Jaschan.
B．They are Jaschan's friends.
C．They are computer viruses.
D．They threaten computer security.