What are advantages of using semaphores over ordinary shared variables for synchronization? Mark all that apply.

If a lower priority process holds the semaphore, a high priority process that tries to acquire it will allow the lower priority process to execute and free the semaphore

Semaphore access routines are provided by the OS and so are less likely to have coding errors in them

Programmers are relieved of having to remember to lock and release resources - this is done automatically by the system

A process that cannot obtain the desired resource will not use the CPU until it can obtain the desired resource

The entry and exit routines execute more efficiently than the corresponding spin lock routines