Correct option is C
The correct improvement for the highlighted part of the sentence
"Using seeds for grow more plants is an exceptionally good way of gardening." is
"to grow more plants."
· The corrected phrase
"to grow more plants" uses the infinitive form "to grow," which is grammatically appropriate after prepositions and in the context of expressing the purpose or intention of an action.
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Explanation: The infinitive form here clearly states the purpose of using seeds in gardening, which is to grow more plants.
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Other options:
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(a) "No improvement" does not correct the grammatical error.
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(b) "to growing more plants" and
(d) "for grows more plants" are grammatically incorrect.