READ THE TEXT AND FILL IN EACH GAP WITH ONE SUITABLE WORD

1. Read the text and fill in each gap with one suitable word. (15 pts) Throughout the ages, the (1) ____________ of the earth has been built up in some places and worn down in other places. The wearing down of the land is called erosion. Wind, water, air, ice and heat all help to (2) ____________ erosion. As the wind blows over the land, it often picks up small grains of sand. When these grains of sand strike (3) ____________ solid rocks, the rocks are slowly worn away. Later, the wind may pick up these new rock particles, and with them wear away other rocks. In this way even very (4) ____________ rocks are worn away by the wind. When articles of rock or soil become (5) ____________ in any way, running water carries them down the hillsides. Some rock and soil particles are carried into streams. The streams may then carry them into the (6) ____________ Land that is covered with trees, grass and other plants wears (7) ____________ very slowly, and so (8) ____________ very little of its soil. The roots of plants help to hold the rocks and soil in place. When rain falls in a forest, the leaves of the trees and the soft soil beneath them are able to hold a great deal of water. Water that falls on grasslands runs away more slowly than does water that falls on (9) ____________ ground. Water that flows slowly carries fewer soil (10) ____________ than water that flows rapidly. Thus, forests and grasslands help to slow down erosion. Even (11) ____________ the land is thickly covered with plants, some erosion goes on. Sometimes there is a long period of rainy weather. In Spring the (12) ____________ snow turns to large quantities of water. At these times the soil cannot (13) ____________ all the water. It then runs down hill in streams. As the streams carry away some of the soil, the stream (14) ____________ gets deeper and deeper. After thousands of years of such (15) ____________, wide valleys are often formed.