2014托福考试阅读模拟试题训练（17）

　　The mineral particles found in soil range in size from microscopic clay particles to large boulders. The most abundant particles—sand, silt, and clay—are the focusof examination in studies of soil texture. Texture is the term used to describe theline composite sizes of particles in a soil sample, typically several representative handfuls.(5) To measure soil texture, the sand, silt, and clay particles are sorted out by size andweight. The weights of each size are then expressed as a percentage of the sample　weight.

　　In the field, soil texture can be estimated by extracting a handful of sod andsqueezing the damp soil into three basic shapes; (1) cast, a lump formed by squeezing　(10) a sample in a clenched fist; (2) thread, a pencil shape formed by rolling soil between the palms; and (3) ribbon, a flatfish shape formed by squeezing a small sample between the thumb and index finger. The behavioral characteristics of the soil when molded into　each of these shapes, if they can be formed at all, provides the basis for a general　textural classification. The behavior of the soil in the hand test is determined by the　(15) amount of clay in the sample. Clay particles are highly cohesive, and when dampened,behave as a plastic. Therefore the higher the clay content in a sample, the more refined　and durable the shapes into which it can be molded.

　　Another method of determining soil texture involves the use of devices called sediment sieves, screens built with a specified mesh size. When the soil is filtered (20) through a group of sieves, each with a different mesh size, the particles become grouped in corresponding size categories. Each category can be weighed to make a　textural determination. Although sieves work well for silt, sand, and larger particles,they are not appropriate for clay particles. Clay is far too small to sieve accurately;　therefore, in soils with a high proportion of clay, the fine particles are measured on the(25) basis of their settling velocity when suspended in water .Since clays settle so slowly,　they are easily segregated from sand and silt. The water can be drawn off andevaporated, leaving a residue of clay, which can be weighed.

　　23. What does the passage mainly discuss?

　　(A) Characteristics of high quality soil

　　(B) Particles typically found in most soils

　　(C) How a high clay content affects the　texture of soil

　　(D) Ways to determine the texture of soil

　　24. The author mentions "several representative

　　(A) the range of soil samples

　　(B) the process by which soil is weighed

　　(C) the requirements for an adequate soil sample

　　(D) how small soil particles are

　　25. The phrase "sorted out" in line 5 is closest in　meaning to

　　(A) mixed

　　(B) replaced

　　(C) carried

　　(D) separated

　　26. It can be inferred mat the names of the three　basic shapes mentioned in paragraph 2 reflect

　　(A) the way the soil is extracted

　　(B) the results of squeezing the soil

　　(C) the need to check more than one handful

　　(D) the difficulty of forming different　shapes

　　27. The word "dampened" in line 15 is closest in　meaning to

　　(A) damaged

　　(B) stretched

　　(C) moistened

　　(D) examined

　　28. Which of the following can be inferred from　the passage about a soil sample with little or　no clay in it?

　　(A) It is not very heavy.

　　(B) It may not hold its shape when molded.

　　(C) Its shape is durable

　　(D) Its texture cannot be classified

　　29. The word "they" in line 23 refers to

　　(A) categories

　　(B) sieves

　　(C) larger particles

　　(D) clay particles

　　30. It can be inferred from the passage that the sediment sieve has an advantage over the hand test in determining soil texture because

　　(A) using the sieve takes less time

　　(B) the sieve can measure clay

　　(C) less training is required to use the sieve

　　(D) the sieve allows for a more exact measure

　　31. During the procedure described in paragraph 3, when clay particles are placed into water　they

　　(A) stick to the sides of the water container

　　(B) take some time to sink to the bottom

　　(C) separate into different sizes

　　(D) dissolve quickly

　　32. The word "fine" in line 24 is closest in　meaning to

　　(A) tiny

　　(B) many

　　(C) excellent

　　(D) various

　　33. All of the following words are defined in the　passage EXCEPT

　　(A) texture (line 3)

　　(B) ribbon (line 11)

　　(C) sediment sieves (line 19)

　　(D) evaporated (line 27)

　　参考答案： DAD BCBBD BA