Ça vs C'est vs Il est

Question

I have read the lessons on all these.   In a quiz, asking me to translate "It's getting on my nerves," I chose "Il est" because "it's" must be referring to something specific.  We don't know what, but no one says generally "It's getting on my nerves" without "it's" referring to something specific.  The correct answer is given as "Ça".  Even if "it's" was referring to something general, why would it be "Ça" instead of "C'est"?

Accepted Answer

Hi Chapel,
You could say -
C’est énervant! = It’s annoying!
But 
Ça  m’énerve! =  It gets on my nerves !(It’s annoying!) 
Or 
C’est ennuyeux = It’s boring
Mais 
Ça m’ennuie = It bores me ( it’s boring) 
Hope this helps!

Answer

I do not understand why, and also see the disconnect between "Il est" not always being used in the specific situation.