The correct answer is D. No improvement.
The phrase “for the past” is used to indicate a period of time that has already passed. In this case, the orphans have been clamouring for nutritious food for two weeks. Therefore, the phrase “for the past two weeks” is correct.
The phrase “since the past” is not idiomatic. It is more common to say “since” followed by a specific date or event. For example, “I have been working here since January.”
The phrase “for past” is not grammatically correct. The correct phrase is “for the past.”
Therefore, the correct answer is D. No improvement.