Which of these correctly identifies a difference between the way BPDUs are handled by 802.1w
and 802.1 D?

A.
802.1 D bridges do not relay

B.
802.1w bridges do not relay BPDUs

C.
802.1D bridges only relay BPDUs received from the root

D.
802.1w bridges only relay BPDUs received from the root.

Explanation:
A bridge sends a BPDU frame using the unique MAC address of the port itself as a source
address, and a destination address of the STP multicast address 01:80:C2:00:00:00.
There are three types of BPDUs:
Configuration BPDU (CBPDU), used for Spanning Tree computation
Topology Change Notification (TCN) BPDU, used to announce changes in the network topology
Topology Change Notification Acknowledgment (TCA)
BPDU are Sent Every Hello-Time
BPDU are sent every hello-time, and not simply relayed anymore. With 802.1D, a non-root bridge
only generates BPDUs when it receives one on the root port. In fact, a bridge relays BPDUs more
than it actually generates them. This is not the case with 802.1w. A bridge now sends a BPDU
with its current information every <hello-time> seconds (2 by default), even if it does not receive
any from the root bridge.

http://www.cisco.com/en/US/tech/tk389/tk621/technologies_white_paper09186a0080094cfa.shtml
#topic4