This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
Which antibody is diagnostic of mixed connective tissue disease 
Select and explain. 
A. Anti-histidyl t-RNA synthetase, B. Anti-U1-ribonucleoprotein, C. Anti-Myeloperoxidase, D. Anti-Proteinase-3
B: Anti-U1-ribonucleoprotein
Answer: B: Anti-U1-ribonucleoprotein 
Explanation: Anti-U1-ribonucleoprotein - MCTD
Anti-histidyl t-RNA synthetase - Inflammatory myopathies.