To avoid known vulnerabilities in authentication and key management of Wi-Fi Protected Setup, what security precaution should be taken?

A.
A PIN must not be reused when an authentication fails between an Enrollee and a Registrar.

B.
Communication between an Enrollee and a Registrar on Interface E must be done via a proxy.

C.
Authentication must always take place via an out-of-band method.

D.
Every device must have a unique PIN which is longer than 8 alphanumeric characters.

E.
An access point without a display should never be used as a Registrar.