2014年4月托福考试模拟试卷及答案(第二套)_第3页

　Questions 23-33

　　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 focus

　　of examination in studies of soil texture. Texture is the term used to describe the

　　line 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 and

　　weight. 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 and

　　squeezing 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 and

　　evaporated, 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

　　handrals" in line 4 in order to show

　　(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)