Which IEEE protocol defines the Spanning Tree protocol?

A.
IEEE 802.1D

B.
IEEE 802.11

C.
IEEE 802.5

D.
IEEE 802.3

Explanation:
The 802.1D spanning tree protocol is an Ethernet link-management
protocol that provides link redundancy while preventing routing
loops. Since only one active path can exist for an Ethernet network to
route properly, the STP algorithm calculates and manages the best
loop-free path through the network.
IEEE 802.5 specifies a token-passing ring access method for LANs.
IEEE 802.3 specifies an Ethernet bus topology using Carrier Sense Multiple
Access Control/Carrier Detect (CSMA/CD).
IEEE 802.11 is the IEEE standard that specifies 1 Mbps and 2 Mbps wireless connectivity in the
2.4 MHz ISM (Industrial, Scientific, Medical) band.
Source: Designing Network Security by Merike Kaeo (Cisco Press, 1999).