单项选择题

It is because of ______ that dolphins seldom sleep according to some scientists' research findings.

A．their stupidity
B．their vulnerability
C．the possible dangers in the ocean
D．their small size
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单项选择题
Predators are ______.
A．able to prey even when they are in deep dream sleep
B．more likely to experience dream sleep
C．incapable of preying when immobilized by dreamless sleep
D．good at preying on stupid animals
单项选择题
Which of the following might be the best title for this passage
A．Scenery and Culture.
B．Traveling in New Zealand.
C．Movies of Imaginary World.
D．The Kingdom of Rohan.
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