Customers can store only iWork files and PDFs. And if they make a change to a file on one device, it's automatically updated on all their devices.
Customers can store any kind of file from any app across all their devices. And if they make a change to a file on one device, it's automatically updated on all their devices.
(C) Customers can back up their entire iPhone on iCloud Drive. And if they lose their phone, they can easily retrieve the backup.
(D) Customers can store only files from enabled apps. And if they make a change to a file on one device, it's automatically updated on all their devices.