The role of active cytotoxic t cells is to attack see concept 43.3 (page)

The answer would be: body cells that have been infected

Cytotoxic comes from word cyto- which mean cells and toxic which mean poison. That means cytotoxic cells will be poisonous to the cells. Cytotoxic t cells roles are to attack cells that infected by pathogens. Some pathogens hide inside the cells so that they won't captured by the leucocytes. 
Cytotoxic t cells destroy such cells so the pathogens inside them could be killed.

Molecules called lipids have long hydrocarbon chains that determine the way they act. they can be fats, oils, or hormones, and even exist in our cell membranes