In ios and android, whats the first thing you should try when troubleshooting a misbehaving app?

A. Check for an app that is using a lot of battery.
B. Uninstall apps, one at a time, starting with the least recently used app.
C. Close apps, one at a time, starting with the foreground app.
D. Close apps, one at a time, starting with the least recently used app.