The thermoneutral zone is defined as: the region of the body halfway between the high-temperature core and the low-temperature skin. the environmental temperature range in which shivering, changes in blood flow, and changes in thyroid hormone concentrations can maintain homeostasis of the body's core temperature. the core body temperature at which no energy is expended to maintain homeostasis. the environmental temperature range over which the changes in skin blood flow alone can regulate body temperature. the region in the central core of the body where temperature never changes.

Which is an advantage of having memory cells when a pathogen is encountered for a second time. a) the memory cells are what proliferate into clones of cells in response to the binding of an antigen. b) memory cells are vital to the primary immune response in that they immediately recognize pathogens even at the first encounter. c) memory cells are essentially effector cells that are short lived and attack antigens even without having a receptor specific to that antigen. d) it ensures that more lymphocytes with a receptor specific to a particular antigen will be present than in a host that had never encountered that pathogen.