2. 外语
  3. The groundwater system is similar to a river system. Therefore, instead of having channels that 【M1】______ connect different par

The groundwater system is similar to a river system. Therefore, instead of having channels that 【M1】______ connect different par

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问题     The groundwater system is similar to a river
system. Therefore, instead of having channels that 【M1】______
connect different parts of the drainage basin, the
groundwater system has connecting pores. Some soils
and rock have connecting pores where water can move 【M2】______
through. Soils and rock are permeable and water can 【M3】______
pass through them this way. Sandstone is a common
permeable rock.
    Soil or rock that have many large connected pores 【M4】______
is very permeable. Water can pass through it easily. Soil
or rock that has few or small pores is not permeable 【M5】______
because water can’t easily pass through. Some material,
such as clay, has very small pores or no pores at all.
Water can’t pass through this impermeable material.
    How deep into Earth’s crust do you suppose
groundwater can go? That depends on the permeability
of soil and rock. Groundwater will keep going to lower 【M6】______
elevations until it reaches a lay of impermeable rock. 【M7】______
When this happens, the impermeable rock acts like a
dam and the water can’t move down any deep. So, it 【M8】______
begins filling up the pores in the rocks over the 【M9】______
impermeable layer. A layer of permeable rock that
transmits water freely is an aquifer. The area where all
of the pores in the rock are completely filled in water is 【M10】______
the zone of saturation. The upper surface of this zone is
the water table.
【M1】
选项
答案Therefore—However
解析 篇章错误。此处承接第一、二句，连接词的使用取决于这两句话间的关系。第一句说的是“地下水与河流水系的相似之处”，后一句则提出“在水系各部分的连接方式上两者存在差异”，因此这两句话不是因果关系，therefore显然不合适。
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