Explanation:

- Statement 1: "One must" is correct. It sets the context of a general rule.

- Statement 2: "keep up" is correct. It indicates the action of fulfilling or maintaining.

- Statement 3: "his promise" is incorrect. The subject "One" should be followed by "their promise" for gender neutrality and subject-verb agreement.

- Statement 4: "No error" is incorrect, as previously identified.

- Option 1: Incorrect. It corresponds to Statement 1.

- Option 2: Incorrect. It refers to Statement 2.

- Option 3: Correct. It indicates the error in Statement 3.

- Option 4: Incorrect. Suggests no error, but there is an error.