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
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.
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
答案是A，为什么啊，我选的是D，什么叫handrals？？
恰巧昨晚也做了00－1，这个肯定是A啦，指土样的Texture～你看的是电子版的？那个不是handrals，应该事handfuls，指的是用手抓一把。至于什么是“用手抓一把”呢，可以参看第二段。看楼主问这个问题，大概这篇文章没看懂吧^_^
题目中 就是有 原题错误。
避免不了。还耽误事情。
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