There are often not more than one or two independent variables tested in an experiment, otherwise it is difficult to determine the influence of each upon the final results. There may be several dependent variables, because manipulating the independent variable can influence many different things.
Well, we can rule out diffusion and osmosis because these are passive processes, so we're left with A and C. I'd say A, because the energy is used in muscle contraction.
The segments of DNA that code for specific traits are called genes