Question: What triggers the measurement of the number of attempted additions of LWA DRB in an E-UTRAN network?
Option 1: Transmission of RRCConnectionReconfiguration message with drb-ToAddModList containing at least one new LWA DRB identity.
Option 2: Receipt of a new UE configuration from the eNB.
Option 3: Detection of packet switched traffic on the EPS bearer.
Option 4: Activation of WLAN mobility features.
Explanation: According to the text, the measurement is triggered when the eNB transmits an RRCConnectionReconfiguration message that includes a drb-ToAddModList with at least one new LWA DRB identity (drb-TypeLWA set to TRUE). This indicates an attempt to add a new LWA DRB to the UE's configuration.