The correct answer is A. watering.
The sentence is in the present perfect continuous tense, which is used to talk about an action that started in the past and is still happening now. The verb “water” is an action verb, so it needs to be in the present participle form, which is “watering.”
The other options are incorrect because they are not in the present participle form. Option B, “watered,” is the past tense form of the verb “water.” Option C, “waters,” is the third person singular present tense form of the verb “water.” Option D, “none,” is not a verb.
Here is a diagram that shows the different verb forms:
Tense | Form | Example
——- | ——– | ——–
Present | -s/-es | He waters the plants.
Present continuous | -ing | He is watering the plants.
Past | -ed | He watered the plants.
Past continuous | -ing | He was watering the plants.
Future | will + base form | He will water the plants.
Future continuous | will be + -ing | He will be watering the plants.
I hope this helps!