Which of these is a mobile operating system?

Android is better than iOs, IMHO.

Windows can be a mobile OS too. Relatively recently - Windows Phone which was running on Lumia phones. These were made by Nokia, but later by the MS and branded Microsoft. Windows Mobile was older platform, running on PDA devices for example.

QuizzLand is made by Android.

Vlad, It's funny how things went. MS dominated the desktop with MSDOS. Apple had the first popular consumer graphical interface with the Mac, but Windows won most of the consumer market, over Mac and Linux. MS had IE, but Chrome won the browser wars. MS was late on phones and eventually Google beat everyone. Apple or MS could have ruled everything but Apple is IMO too expensive and more of a status brand. MS failed to see the future fast enough and now the digital world is pretty much at Google's mercy, for better or worse.

Why did the Android phone bring a ladder to the Apple store? To reach the iCloud and prove it’s got higher standards!

windows phone is a thing although it is extinced

Technically both Android and Windows are valid, although Windows Mobile was discontinued.

Nor a fan of that system.

Maybe too easy...