What is one advantage of using EAP-TTLS instead of EAP-TLS as an authentication mechanism in an 802.11 WLAN?

What is one advantage of using EAP-TTLS instead of EAP-TLS as an authentication mechanism in an 802.11 WLAN?
A . EAP-TTLS sends encrypted supplicant credentials to the authentication server, but EAP-TLS uses unencrypted user credentials.
B . EAP-TTLS supports client certificates, but EAP-TLS does not.
C . EAP-TTLS does not require an authentication server, but EAP-TLS does.
D . EAP-TTLS does not require the use of a certificate for each STA as authentication credentials, but EAP-TLS does.

Answer: D