If a thread attempts a wait$()$ operation when a counting semaphore has been decremented to zero, the thread $q,$

obtains a resource from the pool and the semaphore remains equal to $0$

obtains a resource from the pool and decrements the semaphore to $1$

returns a resource to the pool and increments the semaphore to $1$

must wait until a resource is returned to the pool by a signal$()$ operation