HELP ! can someone please explain to me on how to set it up ?

The correct answer is -

4/4

100%

Explanation:

In this question, it is given that allele B (blue) is dominant over allele b (purple) and both Randal and cell have the same genotype of recessive alleles that is bb and bb.

The offspring of these two will be the same as the due to gametes Randall and cella produce are same which is b and b.

      b    b

b    bb   bb

b    bb    bb

here all four out of four have the same purple skin with 100% chances.

i believe it would cause an increase of percipitation, though i could be wrong. so i would say b is the answer.

"d.) carbon dioxide and hydrogen sulfide"