¡¡¡¡28.It can be inferred from the third paragraph that the sleeping habits
¡¡¡¡of most Americans have changed since the 1700 s in all the following ways EXCEPT
¡¡¡¡£¨A£© the position in which people sleep
¡¡¡¡£¨B£© the numbers of bolsters or pillows people sleep on
¡¡¡¡£¨C£© the length of time people sleep
¡¡¡¡£¨D£© the number of people who sleep in one bed
¡¡¡¡29.The word "afforded" in line 33 is closest in meaning to
¡¡¡¡£¨A£© provided
¡¡¡¡£¨B£© spent
¡¡¡¡£¨C£© avoided
¡¡¡¡£¨D£© absorbed
¡¡¡¡30.Which of the following was most likely to be found in a bedroom in the colder areas of the American colonies£¿
¡¡¡¡£¨A£©A linsey-woolsey
¡¡¡¡£¨B£©A vent from a central healing system
¡¡¡¡£¨C£©A fireplace
¡¡¡¡£¨D£©A wood stove
¡¡¡¡Questions 31-40
¡¡¡¡Growing tightly packed together and collectively weaving a dense canopy of branches£¬ a stand of red alder trees can totally dominate a site to the exclusion of almost everything else. Certain species such as salmonberry and sword ferns have Line adapted to the limited sunlight dappling through the canopy£¬but few evergreen trees £¨S£© will survive there£» still fewer can compete with the early prodigious growth of alders. A Douglas fir tree reaches its maximum rate of growth ten years later than an alder£¬ and if the two of them begin life at the same time£¬the alder quickly outgrows and dominates the Douglas fir. After an alder canopy has closed£¬ the Douglas fir suffers a marked decrease in growth£¬ often dying within seven years. Even more shade-tolerant species of trees such as hemlock may remain badly suppressed beneath aggressive young alders.
¡¡¡¡Companies engaged in intensive timber cropping naturally take a dim view of alders suppressing more valuable evergreen trees. But times are changing£» a new generation of foresters seems better prepared to Include in their management plans consideration of the vital ecological role alders£¬ play. Among the alder s valuable ecological contributions is its capacity to fix nitrogen in nitrogen-deficient soils. Alder roots contain clusters of nitrogen-fixing nodules like those found on legumes such as beans. in addition£¬ newly developing soils exposed by recent glacier retreat and planted with alders show that these trees are applying the equivalent of ten bags of high- nitrogen fertilizer to each hectare per year. Other chemical changes to soil in which they are growing Include a lowering of the base content and rise In soil acidity£¬ as well as a substantial addition of carbon and calcium. to the soil.
¡¡¡¡Another important role many alders play in the wild£¬ particularly in mountainous areas£¬ is to check the rush of water during spring melt. In Japan and elsewhere£¬ the trees are planted to stabilize soil on steep mountain slopes. Similarly£¬alders have been planted to stabilize and rehabilitate waste material left over from old mines£¬ flood deposits£¬ and landslide areas in both Europe and Asia.
¡¡¡¡31.What does the passage mainly discuss£¿
¡¡¡¡£¨A£©Differences between alder trees and Douglas fir trees
¡¡¡¡£¨B£©Alder trees as a source of timber
¡¡¡¡£¨C£©Management plans for using alder trees to improve soil
¡¡¡¡£¨D£©The relation of alder trees to their forest environments
¡¡¡¡32.The word "dense" in line I is closest in meaning to
¡¡¡¡£¨A£© dark
¡¡¡¡£¨B£© tall
¡¡¡¡£¨C£© thick
¡¡¡¡£¨D£© broad
¡¡¡¡33.Alder trees can suppress the growth of nearby trees by depriving them of
¡¡¡¡£¨A£© nitrogen
¡¡¡¡£¨B£© sunlight
¡¡¡¡£¨C£© soil nutrients
¡¡¡¡£¨D£© water
