What disadvantage does EAP-TLS have when compared with PEAPv0 EAP/MSCHAPv2 as an 802.11 WLAN security solution?

What disadvantage does EAP-TLS have when compared with PEAPv0 EAP/MSCHAPv2 as an 802.11 WLAN security solution?
A . Fast/secure roaming in an 802.11 RSN is significantly longer when EAP-TLS is in use.
B . EAP-TLS does not protect the client’s username and password inside an encrypted tunnel.
C . EAP-TLS cannot establish a secure tunnel for internal EAP authentication.
D . EAP-TLS is supported only by Cisco wireless infrastructure and client devices.
E . EAP-TLS requires extensive PKI use to create X.509 certificates for both the server and all clients, which increases administrative overhead.

Answer: E