单项选择题

The fourth paragraph of the passage primarily discusses ______.

A．the reproduction of sea cucumbers
B．the food sources of sea cucumbers
C．the eating habits of sea cucumbers
D．threats to sea cucumbers' existence
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单项选择题
What can be inferred about the defence mechanisms of the sea cucumber
A．They are very sensitive to surrounding stimuli.
B．They are almost useless.
C．They require group cooperation.
D．They are similar to those of most sea creatures.
单项选择题
Which of the following would NOT cause a sea cucumber to release its internal organs into the water
A．A touch.
B．Food.
C．Unusually warm water
D．Pollution.
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