How are introns and exons distinguished during splicing?
A. The RNA polymerase pauses transcription at the intron junctions and begins transcription at the beginning of the next available exon.
B. The spliceosome looks for an intact open reading frame.
C. The ribosome pauses translation at the beginning of the intron and resumes translation at the beginning of the next available exon.
D. The spliceosome identifies conserved features at the splice sites and within the intron.