Early in the ancient times, farmers did experiments(improve)______ the agricultural productivity.

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问题 Early in the ancient times, farmers did experiments(improve)______ the agricultural productivity.

选项

答案to improve。

解析 根据句子结构判断,空格处应为动词不定式作目的状语,所以空格处应填入improve对应的动词不定式形式to improve。
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