The question asks to measure web page load times in a user's browser for a web application running in Azure. Application Insights in Azure Monitor (Option B) is specifically designed for application performance monitoring (APM) and includes client-side monitoring capabilities that track page load times, user interactions, and performance metrics directly from the browser. This is confirmed by the community discussion, where Option B has 100% consensus and upvoted comments explain that Application Insights automatically detects performance anomalies and analyzes user behavior. Option A (Azure Monitor alerts) is for notifications based on predefined conditions, not direct measurement. Option C (Log Analytics) is for querying and analyzing log data, not real-time page load tracking. Option D (Azure Network Watcher) focuses on network infrastructure monitoring for IaaS resources, not application-level web analytics.