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Answer:
In optics, the refractive index of a material is a dimensionless number that describes how fast light travels through the material. It is defined as n={\frac {c}{v}}, where c is the speed of light in vacuum and v is the phase velocity of light in the medium
Its true as you breath your heart and lungs go in and out as if you were swinging a door open and shut letting oxgen in and out hope i could help :)
Answer:
A substrate is a molecule upon which an enzyme acts. The substrate is changed by the reaction and, in this case, two products are made. A reactant and substrate have the same meaning. The term reactant is more often used in chemistry. Biology Science
Explanation: