Read the following text and choose the right forms of the missed words (they are given below the text)

Providing artificial drainage

Under many conditions, water drains from soil 1)______. However, a flood or heavy rain can cause excess water 2) ______ in soil. An efficient water 3) ______ system provides for the artificial drainage of excess water.

When land 4) ______ too much water, the water table rises almost to the level of the ground surface, and the soil becomes 5) ______. Most plants need air in the soil, as well 6) _____ water. Pores (air spaces) in soil 7) ______ provide air. However, 8) ______ of saturated soil are filled with water.

Farmers 9) ______ water from soil through underground drains or by means of ditches. Underground drains are made 10) _____ pipe or hollow tile. They have 11) ______ openings that allow water to enter but keep soil out. Drainage ditches cost less to build than underground drains, but they are expensive 12) ______. They also interfere with 13) _______ of workers and machines. Some drainage systems return water to irrigation channels for 14) ______.

Most irrigation water contains small amounts 15) _____ soluble salts. These salts remain in the soil, whether crops use the water or it 16) ______ from the surface of the ground. Excess salts 17) ______ reduce or prevent plant growth. For example, certain salts react 18) _______ with soil particles to change the structure of soil. Such a change can 19) ______ the movement of air and water through the soil. In addition, salts injure some plants and compete 20) _______ roots for water in soil.

Farmers remove excess salts from soil by 21) _______ (flushing) the soil with water. Leaching applies 22) _______ water to soil to move salts away from the roots of plants. But if the land 23)_______ a good drainage system, leaching may result in saturated soil. In addition, 24) _______ leaching may not remove enough salt In the Southwestern United States, some land that 25) _______ is now of limited use for agriculture because of a build-up of salt.

1) A. naturally B. nature C. natural

2) A. to be accumulated B. to accumulate C. to have accumulated

3) A. to manage B. managerial C. management

4) A. receives B. will receive C. received

5) A. saturation B. saturated C. saturating

6) A. such B. so C. as

7) A. normally B. normal C. normability

8) A. porous B. the pores C. porosity

9) A. to remove B. removes C. remove

10) A. of B. up C. down

11) A. number B. numerous C. numerously

12) A. maintenance B. maintaining C. to maintain