Final answer:
The variable region of the T-cell receptor is responsible for binding to specific antigens, while the constant region anchors the receptor to the cell surface.
Step-by-step explanation:
The correct answer to the question regarding the T cell receptor is e. variable; constant.
The variable region of the α and β chains of the T-cell receptor forms the pathogen-specific binding site, which is essential for the immune system's ability to recognize a diverse array of antigens. This region gets its name because the amino acid sequence varies between different T-cell receptors, endowing each T cell with specificity for a particular antigen. Conversely, the constant region of the α and β chains serves to anchor the molecule on the cell surface and exhibits less variability between different receptors.