During the adaptive response, the MHC molecules are responsible for presenting an antigen to T cells. The two types of MHC (MHCI and MHCII) have specific roles during the response. Which of the following most accurately describes the characteristics of MHCII molecules in mounting the antibody response?
a. found on all nucleated cells, present endogenous antigens, activate cytotoxic T cells
b. found on APC, present exogenous antigens, activate cytotoxic T cells
c. found on APC, present endogenous antigens, activate T helper cells
d. found on APC, present exogenous antigens, activate T helper cells

Hunting in the darksome fish rely on senses beyond sight. in the darkness of the marianas trench, a fish called the rattail has an extremely sensitive sense of smell. the fish uses scent, rather than sight, to steer toward food. once it's near food, the rattail uses a special organ on the bottom of its chin to guide itself by feel.marine snowone staple of the deep sea diet is "marine snow," flakes of organic, edible substances that sink down from the upper ocean. animals at the ocean's bottom find sustenance in everything from the bodies of dead creatures to fecal matter. marine snow is diverse enough to support numerous species. for instance, several species of snails and worms feed exclusively on deceased whales.microorganismsthe deep sea is an intricate ecosystem, and even the ocean floor itself plays a part. hydrothermal vents are cracks in the sea floor where erupting magma mixes with ocean water to produce plumes of hot, sulfur-rich chemicals. some microbes can use these chemicals for energy, sustaining their existence and that of the animals who depend on their roles in the deep sea food chain.