a-removes CO2
b-outside the body
c-transports materials to and from cells
d-inside the body
e-a physiological state in which a stable internal body environment is maintained
f-removes water and minerals (perspiration)
g-must be removed by the body, examples are CO2, water and nitrogen
h-removes undigested food, gas and water
i-removes water and nitrogen containing metabolic waste
options: metabolic waste, gastrointestinal system, urinary system, respiratory [...]