Question

which cells engulf a pathogen and display a fragment of it on their cell surface?
a antigen presenting cells
b activated helper t cells
c activated cytotoxic t cells
d memory t cells

Explanation:

Antigen - presenting cells (APCs) are responsible for engulfing pathogens through phagocytosis or endocytosis, processing them, and then presenting pathogen - derived fragments (antigens) on their cell surface for recognition by T cells. Other cell types listed do not have this primary function of engulfing and presenting pathogen fragments.

Answer:

A. Antigen presenting cells