Refer to the exhibit.

Switch S1 has been configured with the command spanning-tree mode rapid-pvst. Switch S3 has
been configured with the command spanning-tree mode mst. Switch S2 is running the IEEE
802.1D instance of Spanning Tree. What is the result?

A.
IEEE 802.1w and IEEE 802.1s are compatible. IEEE 802.1d is incompatible. Switches S1 and
S3 can pass traffic between themselves. Neither can pass traffic to switch S2.

B.
Switches S1, S2, and S3 can pass traffic between themselves.

C.
Switches S1, S2, and S3 can pass traffic between themselves. However, if the topology is
changed, switch S2 does not receive notification of the change.

D.
IEEE 802.1d, IEEE 802.1w, and IEEE 802.1s are incompatible. All three switches must use the
same standard or no traffic can pass between any of the switches.

Explanation:
A switch running both MSTP and RSTP supports a built-in protocol migration mechanism that
enables it to interoperate with legacy 802.1D switches. If this switch receives a legacy 802.1D
configuration BPDU (a BPDU with the protocol version set to 0), it sends only 802.1D BPDUs on
that port. An MST switch can also detect that a port is at the boundary of a region when it receives
a legacy BPDU, an MST BPDU (version 3) associated with a different region, or an RST BPDU
(version 2).
However, the switch does not automatically revert to the MSTP mode if it no longer receives
802.1D BPDUs because it cannot determine whether the legacy switch has been removed from
the link unless the legacy switch is the designated switch
Reference:
http://www.cisco.com/en/US/docs/switches/lan/catalyst2950/software/release/12.1_9_ea1/configur
ation/guide/swmstp.htm