which way does the Bridge Assurance mechanism modify the default spanning-tree behavior in an effort to prevent bridging loops?

In which way does the Bridge Assurance mechanism modify the default spanning-tree behavior in an
effort to prevent bridging loops?

A.
Received BPDUs are looped back toward the sender to ensure that the link is bidirectional.

B.
If BPDUs are no longer received on a port, the switch immediately sends out a TCN BPDU.

C.
Extended topology information is encoded into all BPDUs.

D.
BPDUs are sent bidirectional on all active network ports, including blocked and alternate ports.