Answer:
The correct answer is A. whoever waters it.
Explanation:
Letter A is the only possible answer because there is no necessity for a comma in the sentence, only for a period in the end. Letter B is not possible because there is a comma separating the preposition "for" from "whoever". In case of letter C it is also not possible because "whoever" is separated by a comma from the verb "waters". And, letter D is also not possible because a comma separanting the verb "waters" from the object "it" is totally wrong.
