Concept:The phrase “stand in for” means to act as a substitute or representative for someone.Explanation:The speaker could not attend the meeting, so Penda was asked to take their place.When you “stand in” for someone, you represent that person in their absence.Therefore, the correct preposition to complete the sentence is “in”.Answer:I asked Penda to stand in for me since I could not attend the meeting.Correct option: C. in.