单项选择题

What is implied by saying "a layer of soil acts as a sponge" (Para. 2)

A．Soil can be used to clean things.
B．Soil can store water and give it up when needed.
C．Soil is all elastic material.
D．Soil can provide water.
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单项选择题
What does this refer to in the sentence This leaves gaps of bare soil... (Para. 4)
A．Cutting down trees and grasses and burning them.
B．The New Stone Age people's clearing of rain forest.
C．Planting of seeds in the bare soil.
D．This type of farming.
单项选择题
The respiration of living things and the food production of plants are______.
A．separate processes
B．complementary
C．opposite
D．interdependent
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