Q$4$: Considering the semaphore $($s$),$ which of the following is correct?

a$.$ Wait operation is used to enter the critical section where $(s_{++})$is used to increment the semaphore.

b$.$ Signal operation is used to enter the critical section where $(s_{++})$is used to increment the semaphore.

c$.$ Single operation is used to exit the critical section where $($S$--)$ is used to decrement the semaphore.

d$.$ Wait operation is used to enter the critical section where $($S$--)$ is used to decrement the semaphore.

e$.$ None of the above.