Hemoglobin is a protein that binds to oxygen. It is only produced by red blood cells and it allows blood to transport oxygen throughout the body. What statement does this information best demonstrate?

A. Proteins with similar functions to those produced in humans can be found in other species.
B. Specialized cells that are grouped together and perform similar functions are called tissues.
C. The proteins produced by cells have structures that are related to their function.
D. Proteins in specialized cells are the result of the expression of particular genes.

D. Proteins in specialized cells are the result of the expression of particular genes.