What is the result when a switch that is running PVST+ is added to this network?

Refer to the exhibit.

What is the result when a switch that is running PVST+ is added to this network?
A . DSW2 operates in Rapid PVST+ and the new switch operates in PVST+
B . Both switches operate in the PVST+ mode
C . Spanning tree is disabled automatically on the network
D . Both switches operate in the Rapid PVST+ mode.

Answer: A

Explanation:

From the output we see DSW2 is running in RSTP mode (in fact Rapid PVST+ mode as Cisco does not support RSTP alone). When a new switch running PVST+ mode is added to the topology, they keep running the old STP instances as RSTP (in fact Rapid PVST+) is compatible with PVST+.