Explanation:

- The original phrase in the sentence is "kept on waiting," which suggests a continuation of waiting.

- Option 1: kept

- This suggests Mohan waited, but it doesn't capture the continuous nature of waiting implied by "kept on."

- It truncates the suggested duration or persistence.

- Option 2: kept to

- This suggests adherence to something, like rules or a plan, and doesn't fit the context of waiting.

- Option 3: kept for

- This suggests intention or purpose, as in keeping something for someone, which isn't relevant to this context.

- Option 4: no correction required

- "Kept on waiting" effectively communicates that Mohan continued to wait.

- It fits the structure and intended meaning well.