The class of RNA molecules linked with proteins in forming the large and small subunits of a cytoplasmic structure is ribosomal RNA (rRNA).

Here's why:

* Ribosomes are the cytoplasmic structures responsible for protein synthesis.

* rRNA molecules are essential components of ribosomes. They provide the structural framework for ribosomes and participate in the decoding of mRNA and the formation of peptide bonds.

* Proteins also play a crucial role in the structure and function of ribosomes. They help to stabilize the rRNA and provide additional catalytic activity.

Together, rRNA and proteins combine to form the large and small subunits of ribosomes. These subunits work together to translate mRNA into protein sequences.