C. bb because the white allele is recessive
Methane is the gas that is strongly correlated with Earth's heating and cooling patterns. Did you know that cow's flatulence is methane gas?! Interesting fact!
Since the male and the female have recessive alleles of this gene, all of their offspring will be like that too.
rr x rr cross will result in 100% of the offspring with the genotype: rr
R- dominant (but none of the parents has this allele)
r- recessive
LOCAL ENVIRONMENT ISSUE:
People dump a lot of trash in the sea, and the sea creatures living there goes through a lot of trouble to live with all the muck getting in them. Of course, don't write it like that in your assignment - you'll get told off for the straight forwardness.