Re: why do we call it DNA instead of DRNA or DRA?

DNA stands for deoxyribonucleic acid and is made up of a 
sugar-phosphate backbone (sugar = deoxyribose) and nucleotides.  You're 
right in that it is a ribose sugar so technically DNA could have a short 
form DRNA in order to account for the specific hydroxyl group on it.  
Deoxyribose is distinct from ribose itself (because of the hydroxyl group); 
DNA is shorter than DRNA; and RNA itself is distinct from DNA; so all 
together I think this is why it is DNA and not DRNA.  As to why not DRA, 
the nucleotide part is the important "instruction" bearing part of DNA.  
With D already representing the sugar, denoting the nucleotide with N is 
more reasonable than leaving it out.  The A is for acid and with it alone, 
it could stand for any acid, but in this case, it is related to the nucleic 
acid.