Operating System (OS)
You should choose sleep option when

The computer is tired after working for the whole day
When computer gets hanged frequently. Let it sleep for some time
You are leaving for a very short time and want to resume you work shortly
You finish working and going to bed

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Operating System (OS)
Semaphores

are used to do I/O
are used for memory management
synchronize critical resources to prevent deadlock
synchronize critical resources to prevent contention
None of these

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