Answer:
color of light
Explanation:
<em>The independent variable is the variable that is supplied and often varied/manipulated by the researcher during the course of experiments. It is varied/manipulated in order to see the effect it will produce on another experimental variable - the dependent variable.</em>
In this case, out of all the variables supplied by Mary, only the color of light supplied was varied - red, white, green, and blue; other variables supplied were kept constant. Hence, <u>the independent variable is the color of light.</u>
D. Phenotype because a phenotype is observable traits
B. Soil Contamination
All the other answers are talking about clean and pure things while this answer is the only negative one. So B is your answer.
Age, Diet, lifestyle choices, environment and RES
