ExplanationThe time triggers after and once indicate that the landscape is no longer arid, so you need a word that means something like not dry and lifeless. Both barren and desolate are nearly the opposite of what you’re looking for, so eliminate choices (B) and (D).
Neither innocuous, which means harmless, nor limpid, which means clear, is supported by the sentence, so eliminate choices (A) and (F). Both verdant and bountiful can mean not dry and lifeless, so choices (C) and (E) give you appropriate, equivalent sentences.
Hence options C and E are correct!
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