Which of the following sentences better explains the concept of a “fallen angel” in terms of creditworthiness of bonds, according to the CFA Institute?

• a) Fallen angels are high-yield (speculative grade) bond issuers whose credit quality has deteriorated in the last 12 months.

• b) Fallen angels are formerly investment-grade issuers whose credit quality has deteriorated since the time of issuance.

• c) Fallen angels are formerly speculative-grade issuers whose credit quality has improved, significantly, since the time of issuance.