a) if a process is executing in its critical section, then no other process must be executing in their critical sections
b) if a process is executing in its critical section, then other processes must be executing in their critical sections
c) if a process is executing in its critical section, then all the resources of the system must be blocked until it finishes execution
d) none of the mentioned

Answer: a
Explanation: Mutual exclusion implies that if a process is executing in its critical section, then no other process must be executing in their critical sections