Which Mechanism Best Describes the Process by Which an Antigen-Presenting

Which mechanism best describes the process by which an antigen-presenting cell triggers an adaptive immune response?

A) Proteins are tethered to the cell cortex.
B) Proteins are tethered to the extracellular matrix.
C) Proteins interact with the proteins on the surface of another cell.
D) Protein movement is limited by the presence of a diffusion barrier.