In human,the Down syndrome is caused by trisomy for which chromosme

Which statement is true according to the passage?

A．Mastectomy used to be considered the only safe course.

B．The chances of survival after a mastectomy are greater than after lumpectomy.

C．Mastectomy can decrease the patients' chances of a care.

D．Most women prefer lumpectomy.

Which statement is true according to the passage?

A．Mastectomy used to be considered the only safe course.

B．The chances of survival after a mastectomy are greater than after lumpectomy.

C．Mastectomy can decrease the patients' chances of a care.

D．Most women prefer lumpectomy.

().

I need to look for some papers to add to my research report.

A. Do you like the library in our school?

B. How many papers have you read so far?

C. Why not comfortably stay at home to log onto the Web?

The process by means of which human beings can arbitrarily make certain things stand for other things may be called the symbolic process.【31】we turn, we see the symbolic process【32】work. For example, stripes on the sleeve can be made to stand for military rank; crossed sticks can stand for a【33】of religious beliefs. There are【34】things that have not a symbolic value.

Almost all fashionable clothes are【35】symbolic. And we select our furniture to【36】as visible symbols of our taste, wealth, and social position. We often choose our houses on the【37】of a feeling that it "looks well" to have a "good address". We trade in perfectly good cars for【38】models not always to get better transportation,【39】to give evidence to the community that we can【40】it.

I once had an eight-year-old car in good running condition. A repairman, who knew the condition of the car, kept【41】me to trade it【42】a new model. "But why?" I asked, "The old car's in【43】still." The repairman answered scornfully, "Yeah, but all you've got is transportation."

Such complicated and apparently【44】behavior. leads philosophers to【48】over "Why can't human beings live simply and naturally?"【46】the complexity of human life makes us look enviously at the relative simplicity of such lives as dogs and cats lead.

Simply, the fact that symbolic process makes complexity possible is no【47】for wanting to【48】to a cat existence. A better【49】is to understand the symbolic process【50】instead of being its victims we become, to some degree at least, its masters.

(31)

A．Whichever

B．Whatever

C．Everywhere

D．However

In an intact plant community, undisturbed by human intervention, the composition of a community is mainly a function of the climate and the type of soil. Today, such original communities are very rare—they are practically limited to national parks and reservations.

Civilization has progressively transformed the conditions determining the composition of plant communities. For several thousand years vast areas of arable land have been hoed, ploughed, harrowed and grassland has been cut or grazed. During the last decades the use of chemical substances, such as fertilizers and most recently of weed killers (herbicides) has greatly influenced the composition of weed communities in farm land.

All selective herbicides have specific ranges of activity. They control the most important weeds but not all the plants of a community. The latter profit from the new free space and from the fertilizer as much as the crop does; hence they often spread rapidly and become weeds unless another herbicide for their eradication is found.

The soil contains enormous quantities of seeds of numerous specie—up to half a million per square meters according to scientific literature—that retain their ability to germinate for decades. Thus it may occur that weeds that were hardly noticed before emerge in masses after the elimination of their competitors. Hence, the knowledge of the composition of weed communities before selective weed killers are applied is not only of scientific interest since the plant species present in the soil in the form. of seeds must be considered as potential weeds. For efficient control the identification of weeds at the seedling stage, i.e. at a time when they can still be controlled, is particularly necessary; for the choice of the appropriate herbicide depends on the composition of the weed community.

The composition of a plant community______.

A．depends on climate and soil type in a virgin environment undamaged by human beings

B．was greatly affected by human beings before they started using chemical substances on the soil

C．was radically transformed by uncivilized human beings

D．refers to plants, trees, climate, type of soil and the ecological environment