Human beings should find a new_______of energy.

单选题

Human beings should find a new_______of energy.

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单选题

Water and air are _______ to human beings. We can not live without them.

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单选题

All human beings depend on the process of ___________ for the removal of certain waste products in the body.

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单选题

Friends might not be always trust-worthy, but dogs are; they have long been regarded as the most _______ company of human beings.

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单选题

Another way to divide the study of geography is to distinguish between physical geography and cultural geography.The former focuses on the natural world;the（ ）starts with human beings and studies how human beings and their environment act upon each other.

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