After iCloud Backup has been turned on, iCloud can automatically back up the iOS device each day over Wi-Fi.

Which of the following criteria must be met before these daily backups can be made automatically?

A. iTunes is open on the host computer.
B. The iOS device is plugged into the host computer via USB.
C. The iOS device is in Airplane Mode.

D. The iOS device is connected to a power source.

Reference: https://support.apple.com/en-us/HT203977