I guess its D im not sure
Answer: Option A
Explanation:
The tertiary structure of the protein is made of multiple domains. Every domain of the protein has different function allotted to them.
The exon is the functional part of the genetic material. The exon is part of DNA which encodes for the part of the mature RNA which is being produced once all the introns have been removed after splicing.
It is the main part which decides the respective domain of the functional protein.