[求教]0001阅读33题

yusy · 发表于 2005-3-10 04:29:00

答案是D(evaporate)?

不是A(texture)么?

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)

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.

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