Correct option is A
The word that can be filled in the blank is ‘ensures’ to make the sentence grammatically and contextually correct.
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‘Ensures’ means to make certain that something will happen or be the case.
• As per the context, organic farming guarantees that nature remains pure and fertile, so “ensures” fits perfectly.
Meanings of other given words and why they are incorrect:
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Contradict – to deny the truth of something; does not fit the meaning.
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Cherish – to hold something dear or protect lovingly; not suitable here.
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Envy – to desire something that someone else has; irrelevant in this context.
• Thus, all the other given words have different meanings and do not fit in the context of the sentence.