Explanation
Negative publicity, a downgrade in the credit rating, a falling stock price are all pointers to potential credit problems, and the counterparty credit monitoring group of a bank should be using these as possible early indicators of an upcoming credit health problem. A decline in the yield of the debt issued by a counterparty means its spread is declining and the health of the credit is actually improving. Therefore a decline in the counterparty's corporate debt yield cannot be used as an indicator of potential credit problems.
Choice 'c' is therefore the correct answer.