Question: What triggers the measurement of "Number of Path Update Successful at Secondary Node Additions" in E-UTRAN?
Option 1: Receipt of an E-RAB modification confirmation message by the MME from MN.
Option 2: Receipt of an E-RAB modification confirmation message by the MN from MME after sending SgNB reconfiguration complete message when path switch is needed.
Option 3: Inter-eNB handover (HO) or intra-eNB HO.
Option 4: Secondary Node (SN) change.
Explanation: According to the text, the measurement of "Number of Path Update Successful at Secondary Node Additions" is triggered when the MN receives an E-RAB modification confirmation message from MME after sending SgNB reconfiguration complete message and path switch is needed. This specific scenario excludes SN change, inter-eNB HO, intra-eNB HO, as mentioned in the text.