What type of RNA is processed to remove introns and join exons?

The correct choice is mRNA, which stands for messenger RNA. During the process of transcription, eukaryotic genes are copied into a precursor mRNA (pre-mRNA) that contains both exons and introns. Exons are the coding sequences that will be translated into proteins, while introns are non-coding sequences that need to be removed during RNA processing.

The processing of pre-mRNA involves a complex series of steps known as splicing, where the introns are cut out and the exons are joined together to form a continuous coding sequence. This spliced mRNA is then transported out of the nucleus into the cytoplasm where it can be translated into a protein.

Other types of RNA listed do not undergo this specific processing. tRNA (transfer RNA) is responsible for bringing amino acids to the ribosome during protein synthesis, rRNA (ribosomal RNA) is a key structural and functional component of ribosomes, and snRNA (small nuclear RNA) plays a role in the splicing process itself but does not become a part of the final mRNA product. Thus, mRNA is the type of RNA specifically processed to remove introns and join exons for protein coding.