I believe the answer is C) reproductive isolation.
Hope this helps!
It's both B.They can never be depleted and C.They are replaceable by natural means.
The answer is codon. The genetic code is redundant as there are multiple codons are make the same protein. The codon table is 64 variants of 3 letter nucleotides that make 20 different proteins. 3 of the 64 codons make 1 stop codon (AUG -Met) and 3 stop codons.
