In a sense, farmers began primitive genetic engineering (at the dawn of) agriculture, (which) they kept seeds (from) their best

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问题 In a sense, farmers began primitive genetic engineering (at the dawn of) agriculture, (which) they kept seeds (from) their best plants, gradually (improving) the quality of successive generations.

选项 A、at the dawn of
B、which
C、from
D、improving

答案B

解析 which应改为when,因为修饰的是时间,即农业的初期。
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