Solution

The correct answer is (B) and (D) Only

EXPLANATION:

• (A) A process always check state of currently executing process to enter critical schema:
  • ​This is not necessarily correct. A process does not always need to check the state of the currently executing process to enter the critical section. It just needs to ensure mutual exclusion i.e. if another process is executing in its critical section, then no other process can enter the critical section.
• (B) Spin locks use busy waiting:
  • This is correct. A spin lock is a type of lock where a thread repeatedly checks if the lock is free. If the lock is not free the thread continues to 'spin' in a loop (hence the name 'spin lock'), checking until the lock becomes free.
• (D) Critical region is a part of program, where shared memory is kept:
  • This is correct, a critical region or a critical section in a program is a place where shared resources, such as shared memory, are accessed. These critical sections need to be protected to prevent race conditions or data inconsistency when the resources are accessed by multiple threads or processes concurrently.
• (E) Printer daemon, continuously checks to see if there are any file to be printed:
  • This is partially correct. While a printer daemon can periodically check for new jobs, saying it "continuously checks" may not be fully representative of how it functions - it often responds to interrupts or other signals generated when a new print job arrives. This depends on the implementation of the software.

So the correct answer is 3) (B) and (D) Only.