Answer: D. Regular watering.
Explanation: a pronoun is a word that can replace a noun or a noun phrase in a sentence. Pronouns are often used to avoid repetition in sentences. "It" is an example of a pronoun, used to replace things. In the given sentence, we have the pronoun "it" replacing the noun "regular watering" we can identify what the pronoun is replacing by asking a "what question" (or who if it is a person), in this case "what does not matter?" and the answer would be "regular watering."
