White Blood Cells could be a possible answer. Not sure if this is multiple choice or not.
Since the particles of gas all try to separate and move into equilibrium when exposed to space, all of the particles have been moved out to a certain ratio of particle per air, if that makes sense. When moved to a bigger space, the concentration of the particles aren't as condensed. So therefore, the particles will move out and put more space in between each particle. They will all be spaced out, and there will be less total particles of gas per square inch of air.
Answer by Mimiwhatsup: A one step process where one atom of helium is generated from four atoms of hydrogen.
Why: "Hydrogen fusion (nuclear fusion of four protons to form a helium-4 nucleus) is the dominant process that generates energy in the cores of main-sequence stars. It is also called "hydrogen burning", which should not be confused with the chemical combustion of hydrogen in an oxidizing atmosphere." (Wikipedia)
Answer:
One advantage of models is that all the mice are exactly alike except for color, enabling the control of all variables except the one being studied. Models are also easier to work with than live mice. One disadvantage of using models is that they do not have the same smell and behaviors as real mice.
Another advantage is that models can be reused for the experiment for a longer period of time with less maintenance.
