Analyze the sentence: "He apologized for his mistake and promised not to repeat on it.''
Step 1: Identify the error
- Part (A) and (B) are correct.
- Part (C) has an error in the phrase "repeat on it.'' The verb "repeat'' does not need the preposition "on'' after it.
- Correct phrase is "not to repeat it.'' The preposition "on'' is unnecessary and incorrect here.
Step 2: Correct sentence
"He apologized for his mistake and promised not to repeat it.''
Conclusion
Error is in part (C).