17. The Drosophila Dscam gene contains 48 alternative forms of exon 6. What is themechanism for having only one exon 6 variant in the mature mRNA?
(A) Splicing factors cannot bind to more than one splicing site due to steric hindrance.
(B) Spliced mRNA with more than one exon 6 variant leads to nonsense-mediatedRNA decay.
(C) The docking site binds to only one selector sequence located upstream of the exon6 variant.
(D) Each exon 6 variant contains different sequences at the splicing sites.
(E) Only the exon 6 variant that recruits enough SR proteins is retained in the mature RNA.