The correct answer is (d) They all have the same DNA.
All the multicellular organisms have same DNA but the different parts of the body has different gene expression.
For example: the same DNA is found in the cells of kidney and liver, but the gene expression for liver results in large number of hepatocytes and the same DNA in the kidney will give rise to nephrons.
This proves that all the cells in the multicellular organisms have same DNA but their expression of protein in different cells are different.
I think that the answer is behavioral isolation because this isolation helps members of the same species identify each other as mates and that's what the emperor penguins do.They call their mate with a specific sound.I'm not 100% sure tho