A constant is something that is kept the same throughout the course of a experiment. So I would guess C) because they are not doing anything special. If it’s not C then it is A. :)
Skin color<span> is due primarily to the presence of a pigment called melanin , which is controlled by at least 6 genes. Both light and dark complexioned people have melanin. However, two forms are produced--pheomelanin , which is red to yellow in</span>color<span>, and eumelanin , which is dark brown to black</span>
Answer:
I think it is the last one
<span>C. nitrogen and hydrogen shoould be your answer
</span>
