In a good experimental design, the part of the experiment that is intentionally changed is the A dependent variable.
B independent variable.
C constant
D control

Constants never change.

Controls typically don't change or they are done by standard means

(like in an experiment where you water plants with sodas, the plant you use water with is the control)

Dependent variables are the outcome of the experiment. This is the result of changing something.

Independent variables are what you are testing. A independent variable is something that is  intentionally altered.

easy way to remember it is that dependent variables depend on what other variables are. so you cant change a dependent variable, but you can change the other variables.

a. as the temperature increases, the kinetic energy of the gas molecules increases & the molecules move faster & further away from each other.

b. if you decrease the temperature of a fixed amount of gas at constant pressure, the combined gas law reduces to charles's law. in this case, volume will also decrease.

not only is it colder, it also becomes darker, less salty, and more dense.