Pay attention it's an A if you thoro 
Be real with your click 
Don't let me C you with the D's cause that's a F if you snitch

from Slaughterhouse – Funkmaster Flex Freestyle Lyrics on Rap Genius

Meaning

Simulation classroom “Hood Class”. A play on the first 5 letters of the alphabet except E because E is not a really a grade in school it skips to F

Translation: Pay attention it’s a A if your thoro (don’t be slippin) Be (B) Real with your click. Don’t let me C (See) you with the D (slang for feds) cuz that’s a F (your fucked) if you snitch

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