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搜尋:bedrock

Have you ever noticed the colour of the water in a river or stream after a heavy rainfall? What do you think caused this change in colour? It is soil that has been washed into the river from the riverbank or from the nearby fieldsComponents of Soil Soil is made up of a number of layers(层),each having its own distinctive colour and texture.The upper layer is known as the litter.It acts like a blanketlimiting temperature changes and reducing water loss.The topsoil layer is made up of small particles of rock mixed with rotten plant and animal matter called humus(腐殖质),which is black and gives the topsoil its dark colourThis layer is usually rich in nutrientsoxygen,and waterBelow the topsoil is the subsoil,a layer that contains more stones mixed with only small amounts of organic matterThis layer is lighter in colour because of the lack of humusBeneath the soil lies a layer of bedrockSoil forms from the bottom up.Over time bedrock is attacked by rain, windfrost, and snow.It is gradually broken down into smaller particles in a process called weatheringPlants begin to grow,and rotten materials enrich the topsoilMost of the soil in Eastern Canada.for example.Was formed from weathered rock that was exposed when the ice disappeared l2.000 years ago. Water Beneath the Soil Surface water collects and flows above the ground in lake, pond, and riversOnce in the soil or rock,it is called groundwaterGravity pulls groundwater through the soil in a process called percolation(渗透).Eventually the water reaches a layer called the water tableUnder this is bedrock through which water cannot percolate. As water percolates downward,it dissolves organic matter and minerals from the soil and carries them to deeper layersThis causes a serious problem because plants require these nutrients for growth. Soil pH Soil can be acidicneutral.or basic.The pH of the soil is determined by the nature of the rock from which it was formed.and by the nature of the plants that grow and rot in it. The acidity of rain and snow can lower the pH of the groundwater that enters the soil.By burning fossil fuels such as coal,oil and gasolinehumans have been contributing to higher levels of acidity in many soilsWhen fossil fuels are burnedgases are released into the air and then fall back to earth as acid rainAcid soil increases the problem of carrying nutrients to lower soil levels.As nutrients are removedsoil is less fertilePlants grow more slowly in acidic soil,and also become easily attacked by diseases
【題組】69.We can infer from the passage that the water table lies
(A)between the topsoil layer and the subsoil layer
(B)in the subsoil layer above bedrock
(C)between the subsoil layer and bedrock
(D)in the bedrock layer beneath the subsoil
編輯私有筆記
答案:C
難度:適中
57. Her belief in Buddhism has established the ______ of her life. She cannot do anything without practicing Buddhism.
(A) bedrock
(B) periphery
(C) triviality
(D) ambivalence
編輯私有筆記
答案:A
難度:適中
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 【站僕】摩檸Morning:有沒有達人來解釋一下?
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