All of the following are mentioned in Paragraph 4 as results of the introduction of the heavy plow EXCEPT
A. a rise in trade with the peoples of Eastern Europe.
B. a change in the standard shape of farm fields.
C. an increase in the communal undertakings of farmers.
D. a decrease in the time needed to prepare fields for planting.
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According to Paragraph 5, what was the benefit of using horses to plow fields instead of oxen？
A. They required less food during the day.
B. They pulled heavier loads.
C. Their necks were less susceptible to strain.
D. They worked faster and longer.
已知函数f(x)具有任意阶导数，且fˊ(x)＝[f(x)]2，则当n为大于2的正整数时，f(x)的n阶导数，则f(n)(x)为()．
A. n![f(x)]n＋1
B. n[f(x)]n＋1
C. [f(x)]2n
D. n![f(x)]2n
What can be inferred from Paragraph 6 about the pheromones of female snakes？
A. They are produced year round.
B. They are species specific.
C. They are only detectable by male snakes.
D. They are the strongest chemical odors.
Which of the sentences below best expresses the essential information in the highlighted sentence in the passage？ Incorrect choices change the meaning in important ways or leave out essential information.
A. Farmers banded together and shared responsibility for protecting the manor and producing food.
B. Peasant populations had no choice but to donate their crops to their lord, for it was he who controlled the military.
C. Most manors of the time were organized similarly, consisting of a number of peasant villages surrounding the lord's estate.
D. In a manor, peasants provided labor and food in exchange for their security, which was guaranteed by a local lord.
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