2016年托福阅读强化模拟试题(一)

　　2016年托福阅读强化模拟试题(一)

　　The geology of the Earth's surface is dominated by the particular properties of water.

　　Present on Earth in solid, liquid, and gaseous states, water is exceptionally reactive. It

　　dissolves, transports, and precipitates many chemical compounds and is constantly

　　Line modifying the face of the Earth.

　　(5) Evaporated from the oceans, water vapor forms clouds, some of which are transported

　　by wind over the continents. Condensation from the clouds provides the essential agent of

　　continental erosion: rain. Precipitated onto the ground, the water trickles down to form

　　brooks, streams, and rivers, constituting what are called the hydrographic network. This

　　immense polarized network channels the water toward a single recepatcle: an ocean.

　　(10) Gravity dominates this entire step in the cycle because water tends to minimize its

　　potential energy by running from high altitudes toward the reference point, that is, sea

　　level.

　　The rate at which a molecule of water passes through the cycle is not random but is a

　　measure of the relative size of the various reservoirs. If we define residence time as the

　　(15) average time for a water molecule to pass throught one of the three reservoirs—

　　atmosphere, continent, and ocean—we see that the times are very different. A water

　　molecule stays, on average, eleven days in the atmosphere, one hundred years on a

　　continent and forty thousand years in the ocean. This last figure shows the importance of

　　the ocean as the principal reservoir of the hydrosphere but also the rapidity of water

　　(20) transport on the continents.

　　A vast chemical separation process takes places during the flow of water over the

　　continents. Soluble ions such as calcium, sodium, potassium, and some magnesium are

　　dissolved and transported. Insoluble ions such as aluminum, iron, and silicon stay where

　　they are and form the thin, fertile skin of soil on which vegetation can grow. Sometimes

　　(25) soils are destroyed and transported mechanically during flooding. The erosion of the

　　continents thus results from two closely linked and interdependent processes, chemical

　　erosion and mechanical erosion. Their respective interactions and efficiency depend on

　　different factors.

　　8. All of the following are example of soluble ions EXCEPT

　　(A) magnesium

　　(B) iron

　　(C) potassium

　　(D) calcium

　　答案：B