Although no one is certain why
migration occurs, there are several theories. One theory claims that prehistoric
birds of the Northern Hemisphere were forced south during the Ice Age. As the
glaciers melted, the birds came back to their homelands, spent the summer, and
then went south again as the ice advanced in winter. In time, the migration
became a habit in spite of the disappearance of glaciers.
Another theory proposes that the ancestral home of all modern birds was
the tropics. When the region became overpopulated, many species were crowded
north. During the summer, there was plenty of food, but during the winter,
scarcity forced them to return to the tropics. A more recent
theory suggests a relationship between increasing daylight and the stimulation
of certain glands(腺)in the birds’ bodies that may prepare them fo A. stopped migrating B. continued migrating C. stayed in the north D. migrated south and stayed there
[单项选择]
Passage One
As one works with color in a practical or experimental way, one is impressed by two apparently unrelated facts. Color as seen is a mobile changeable thing depending to a large extent on the relationship of the color to other colores seen simultaneously. It is not fixed in its relation to the direct stimulus which creates it. On the other hand, the properties of surfaces that give rise to color do not seem to change greatly under a wide variety of illumination colors, usually (but not always) looking much the same in artificial light as in daylight. Both of these effects seem to the due in large part to the mechanism of color adaptation mentioned earlier.
When the eye is fixed on a colored area, there is an immediate readjustment of the sensitivity of the eye to color in and around the area viewed. This A. the eye’s adaptation to color B. the properties of colored surfaces C. the effect of changes in color intensity D. experiments on colored objects
[单项选择] Passage Five
Although no one is Certain why
migration occurs, there are several theories. One theory is based upon the
premise that prehistoric birds of the northen Hemisphere were forced south
during the Ice Age, when glaciers covered large parts of Europe, Asia, and North
America. As the glaciers melted, the birds came back to their homelands, spent
the summer, and then went south again as the ice advanced in winter In time, the
migration became a habit, and now, although the glaciers have disappeared, the
habit continues. Another theory proposes that the ancestral home
of all modern birds was the tropics. When the region became overpopulated, many
species were crowded north. During the summer, there was plenty of food, but
during the winter, scarcity forced them to return to the tropics.
A more recent theory, known as photoperiodism, A. stopped migrating B. continued migrating C. began migrating again D. migrated south and stay there
[单项选择] Passage One
Historically, although the children of
immigrants may have grown up bilingual and bicultural, many did not pass on much
of their parents’ language or culture to their own children. Thus, many
grandchildren of immigrants do not speak the language of the old country and are
"American" by culture. However, in some parts of the country with established
communities that share a common language or culture, bilingualism and
biculturalism continue. This is particularly true in communities where new
immigrants are still arriving. In general, cultural pluralism (多元化) is more
accepted in the United States today than it was in the first half of the
20th century, and many of the school systems have developed bilingual
programs and multicultural curricula. At the close of the
20th century, there seemed to be a rise i A. United Statesians B. Americans C. Latin Americans D. North Americans
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