The correct option is
D It had come to beautify its origin
Rain: "To beautify my origin."
As the given sentence in the direct speech is an incomplete answer, we will give a complete answer in the indirect speech.
For example:
Mom: "What are you doing?" - Mom asked what he was doing.
Raj: "Studying." - Raj answered that he was studying.
Option A - 'To beautify its origin' can't be used as it is similar to the direct speech. We have to write the complete answer in the indirect speech. Thus option A is incorrect.
Option B - 'To beautify my origin' can't be used as it is used in the direct speech. Thus option B is incorrect.
Option C - 'It had come to beautify its origin' can be used here as it answers the question completely in the past perfect tense. The question was in the present perfect tense, hence the answer should be in the past perfect tense. Thus option C is the correct answer.
Option D is incorrect as option C is the correct answer.
'The rain replied that it had come to beautify its origin.'