Help, my son's homework about a/an/the/X

All are possible in the appropriate situation.

Could you elaborate on your answer, Mister Micawber? I'd like to know the appropriate situations.
The rule often taught at school is "play + the + musical instrument". Although as a rule of thumb it serves its purpose, it is not adequate to account for the three possibilities in the sentences above. I'm particulary interested in when to use "I can play piano in the music room."

MM's answer is correct.

Which piano? The one in the music room.

He can play [the] piano really well. Either is fine.

I noticed this issue has been discussed at length before, namely here and here.

hi mister micawber

i didn't know where to write to you privately so I chose to write here...

I asked several questions a couple of years ago and received answers from you which i liked very much...one of them was ".....resembled later helicopters" and ".....looked like an earlier helicopter"

It was a question about Da Vinci's plans. i couldn't understand how "a later he

Hello, Vedat,

Offhand, I would say that they are the same ('should' of course is also used in other ways with other meanings). This language being English, however, there are no doubt places where one collocates and the other does not. None spring to mind, though.