Explanation:

Splicing is a critical process that occurs in eukaryotic cells, where introns are removed from the pre-mRNA molecules and exons are joined together to form mature mRNA. Splicing activity is a function of several types of RNA molecules. Let's look at each of them in detail:

A: mRNA (Messenger RNA)
mRNA is a type of RNA that carries genetic information from DNA to ribosomes, where it is used as a template for protein synthesis. While mRNA is involved in the process of splicing, it is not responsible for the splicing activity.

B: snRNA (Small Nuclear RNA)
snRNA is a type of RNA that is found in the nucleus of eukaryotic cells. It plays a crucial role in the splicing of pre-mRNA molecules. snRNA molecules combine with proteins to form small nuclear ribonucleoproteins (snRNPs), which recognize the splice sites and catalyze the splicing reaction. Thus, snRNA is responsible for the splicing activity.

C: tRNA (Transfer RNA)
tRNA is a type of RNA that carries amino acids to ribosomes during protein synthesis. While tRNA is involved in the process of translation, it is not responsible for the splicing activity.

D: rRNA (Ribosomal RNA)
rRNA is a type of RNA that is a component of ribosomes, which are responsible for protein synthesis. While rRNA is involved in the process of translation, it is not responsible for the splicing activity.

Conclusion:
In conclusion, splicing activity is a function of snRNA, which combines with proteins to form snRNPs that recognize splice sites and catalyze the splicing reaction. Thus, the correct answer to this question is B: snRNA.