Answer: BBB-

### Explanation - **Option A (A-)**: Incorrect. A bond rated A- can be downgraded one category (to BBB-) and still remain within the investment-grade category. - **Option B (BB-)**: Incorrect. A bond rated BB- is already classified as non-investment grade, so a downgrade would not change its status. - **Option C (BBB-)**: Correct. BBB- is the lowest rating within the investment-grade category. A one-category downgrade (from BBB- to BB-) would transition the bond to non-investment grade, aligning with the analyst's concern. This question assesses the understanding of credit rating categories and their implications for bond classification.

Author: LeetQuiz Editorial Team