正解:B
Checking running applications (Option B) is the best first step, as background apps consume CPU, RAM, and battery. Identifying and closing resource-heavy apps can immediately improve performance and battery life.
Uninstall unused programs (Option A): Helps free up storage, but it does not address performance and battery drain as directly as managing running apps.
Update the mobile OS (Option C): Important but may not provide immediate relief, and updates sometimes cause additional issues.
Disable network services (Option D): While turning off features like Wi-Fi or Bluetooth can save battery, it does not directly address slow performance.
Reference: CompTIA A+ Core 2 (220-1102) Exam Objectives - 3.4: Given a scenario, troubleshoot and resolve mobile device issues.