Final answer:
To collect event logs with Azure Monitor, you must enable diagnostics. This is necessary to forward event logs to Azure Monitor Logs or other destinations and provide detailed information about events occurring within Azure resources.
Step-by-step explanation:
To collect data about your Azure infrastructure with Azure Monitor, enabling diagnostics is necessary for certain types of data collection. Among the options provided, the one that requires diagnostics to be enabled is D. Event logs. Usage of web applications, container workload performance, and Linux virtual machine health can be monitored using other Azure Monitor capabilities without necessarily enabling diagnostics. However, to collect event logs, which provide detailed information about events occurring within the Azure resources, enabling diagnostics settings is essential to forward this data to Azure Monitor Logs or other destinations.