2. 考研
  3. Until about four decades ago, crop yields in agricultural systems depended on (1)_____ resources, recycling organic matter, buil

Until about four decades ago, crop yields in agricultural systems depended on (1)_____ resources, recycling organic matter, buil

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问题     Until about four decades ago, crop yields in agricultural systems depended on (1)_____ resources, recycling organic matter, built-in biological control mechanisms and rainfall patterns. Agricultural yields were (2)_____ but stable. Production was (3)_____ by growing more than one crop or variety in space and time in a field as insurance against pest (4)_____ or severe weather. Inputs of nitrogen were (5)_____ by rotating major field crops with legumes. In turn, rotations suppressed insects, weeds and diseases by effectively (6)_____ the life cycles of these pests. A typical corn belt farmer grew corn (7)_____ with several crops including soybeans, and small grain production was intrinsic to maintain livestock. Most of the labor was done by the family with occasional hired help and no (8)_____ equipment or services were purchased from off4arm sources. In these type of farming systems the link between agriculture and ecology was quite (9)_____ and signs of environment degradation were seldom evident.
    But as agriculture modernization (10)_____ the ecology-farming linkage was often broken as ecological principles were (11)_____. In fact, several agricultural scientists have arrived at a (12)_____ consensus that modem agriculture confronts an environment crisis. A growing number of people have become concerned about the long-term (13)_____ of existing food production systems. Evidence has shown that (14)_____ the present capital-and-technology-intensive fanning systems have been extremely productive and competitive, they also bring a (15)_____ of economic, environmental and social problems.
    Evidence also shows that the very nature of the agricultural structure and prevailing polices have led to this environmental (16)_____ by favoring large farm size, specialized production, crop monocultures and mechanization. Today as more and more farmers are integrated (17)_____ international economies, imperatives to (18)_____ disappear and monocultures are rewarded by economies of scale. In turn, lack of rotations and diversification (19)_____ key self-regulating mechanisms, turning monocultures into highly (20)_____ agro-ecosystems dependent on high chemical inputs.
选项 A、external
B、internal
C、exported
D、imported
答案B
解析 考查上下文语义衔接。文章开头就讲以前农业的状况，从后面并列的"循环有机物质，内部生物控制机制和降雨机制"，可以推测农业依赖的是内部资源，选internal，同时注意与本段倒数第二句谈到的 no...equipment or service were purchased from off-farm sources相呼应。排除external"外部的"、imported"进口的"、exported"出口的"。
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