Whats the control variable, manipulated variable, and responding variable?

my group and i did an experiment in biology but i have no idea what the control is or manipulated variable, and i understand the definitions...


we set up milk and were going to tell if fat content had an affect on the time it took for milk to spoil. all we did was take 4 different kinds of milk (2%, 1%, skim milk, and buttermilk) and put them in different containers (each type measured the same and in two containers each, in other words two samples of each kind of milk to observe) so we put them all in the fridge (same temperature) and we started observing them. we took pH levels, and noted changes in each. but how do i tell what the control would be or manipulated variable or responding variable of this kind of experiment?Whats the control variable, manipulated variable, and responding variable?
control: amount of milk-you had a controlled amount


manipulated: fat content-you changed this


responding: pH levels and anything else that changed based on fat content