Question

Read the following passage and mark the letter A, B, C or D on your answer sheet to indicate the correct answer to each of the questions.

    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. 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; cast, a lump formed by squeezing a sample in a clenched fist; thread, a pencil shape formed by rolling soil between the palms; and 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 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 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 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.

It can be inferred from the passage that a soil sample with little or no clay in it ________.

A. may not hold its shape when molded    

B. does not have a classifiable texture

C. is not very heavy       

D. does not have a durable shap

Answer 1

Đáp án A

Có thể suy ra từ đoạn văn rằng một mẫu đất có ít hoặc không có chất sét thì ______.

A. không thể giữ nguyên hình dạng khi được nặn

B. không có kết cấu định dạng được

C. không quá nặng

D. không có hình dạng bền nhất định

“The behavior of the soil in the hand test is determined by the 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.”

(Trạng thái của đất qua thử nghiệm bằng tay được xác định qua lượng chất sét có trong mẫu. Các hạt đất sét có tính kết dính rất cao, và khi được làm ẩm thì có đặc tính như chất dẻo. Vì vậy, lượng đất sét có trong mẫu càng cao thì ta có thể nặn nó thành những hình dạng trau chuốt và giữ được lâu hơn.)

Từ đây ta có thể suy ra mẫu đất ít hoặc không có chất sét sẽ không giữ được hình dạng khi được vắt, nặn. Không thể kết luận liệu nó nhẹ hay nặng, hình dạng bền hay không và kết cấu phân loại được hay không.