Which spanning tree protocol is the IEEE standard that replaced the original Cisco proprietary version?

Correct answer: 802.1w Rapid Spanning Tree Protocol

Option D is correct because IEEE 802.1w is the formal standard designation for Rapid Spanning Tree Protocol, which was developed by the IEEE to replace the original STP and is the direct IEEE-standardized successor that incorporated Cisco's proprietary RSTP concepts. Option A is partially correct in name but is imprecise; RSTP is the common name, while 802.1w is the actual IEEE standard designation being asked about, so Option D is more specific and accurate. Option B, 802.1D, is the original IEEE Spanning Tree Protocol standard that 802.1w replaced, not the replacement itself. Option C, MSTP (802.1s), is a further evolution that maps multiple VLANs to multiple spanning tree instances, which is a distinct standard beyond what replaced the original STP.