more than one device/emulator, please specify the serial number

To specify the serial number of a specific device/emulator, you can use the following command:

adb -s <serial_number> <command>

Replace `<serial_number>` with the actual serial number of the device/emulator you want to target. For example, if you have multiple devices/emulators connected and want to install an APK on a specific device with the serial number "ABC123", you can use:

adb -s ABC123 install app.apk

This way, you can differentiate between multiple devices/emulators connected to your system.