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 environ
A. with
B. to
C. at
D. into
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 environ
A. external
B. internal
C. exported
D. imported
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