This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of nucleic acids, Subject name: Biochemistry
Watson and Crick model is for 
Select and explain. 
A. DNA, B. mRNA, C. rRNA, D. tRNA
A: DNA
Answer: A: DNA 
Explanation: Watson and crick model Double helical structure of DNA.Adjacent bases are seperated by 0.34nm. The diameter or width of the helix is 2 nanometers. Phosphate bonds form the rail of stair case. Bases jutting inside form the steps of staircase. REF :DM VASUDEVAN TEXTBOOK;8th EDITION ;Page no 557.