関連ワード:  what is an operating system class 4    what is an operating system class 4 answer    what is an operating system class 4 worksheet    what is an operating system software class 4    what is an operating system in computer class 4    what is an operating system for class 3    what is meant by an operating system class 4    what is an operating system for class 5    what is an operating system for class 2    what is an operating system for class 6