I ask my teacher is it right to say "it is a brain" or "this is a brain"? He answer me you can say both and I search google and found the same answer that both are correct. But I have some cockroaches in my brain that it should not be this and it at the same time.
Logically as a programmer you can use your awesome brain, the brain is a living organ which is listening your commands and performing through your blood. You can only say a living organ with command THIS until this is alive. You can't say or call a dead brain with command THIS but you call it with command it.
Call Living Brain This.
Call Dead Brain it.