What drawbacks initially prevented the widespread acceptance and use of Opportunistic Key Caching (OKC)?

A: Sharing cached keys between controllers during inter-controller roaming created vulnerabilities that exposed the keys to attackers. B: Because OKC is not defined by any standards or certification body, client support was delayed and sporadic early on. C: Key exchanges during fast roams required processor-intensive cryptography, which was prohibitive for legacy devices supporting only TKIP. D: The Wi-Fi Alliance continually delayed the creation of a client certification for OKC, even though it was defined by IEEE 802.11r.