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: Biochemistry
What is the macromolecular complex that associates with introns during mRNA splicing? 
Select and explain. 
A. Splicer, B. Dicer, C. Nuclear body, D. Spliceosome
D: Spliceosome
Answer: D: Spliceosome 
Explanation: A special multicomponent complex, the spliceosome, is involved in conveing the primary transcript into mRNA. Spliceosomes consist of the primary transcript, five snRNAs (U1, U2, U4, U5, and U6) and more than 60 proteins, many of which contain conserved "RNP" and "SR" protein motifs. Ref: Weil P. (2011). Chapter 36. RNA Synthesis, Processing, & Modification. In D.A. Bender, K.M. Botham, P.A. Weil, P.J. Kennelly, R.K. Murray, V.W. Rodwell (Eds),Harper's Illustrated Biochemistry, 29e.