That is an (a)prokaryote.
Answer: D.) It allows water to resist freezing and thawing cycles.
The ability of the water molecule to absorb and retain heat is called as heat capacity of water, because of this property the temperature of water remains the same for long, irrespective of the external environment. It allows water to resist freezing and thawing cycles because water molecules will resist change in it's temperature. This temperature regulation will prevent instant heating and cooling, hence, will provide suitable environment for the survival of marine organisms.
They can enter your blood stream (via breathing/ingesting) and once in your bloodstream they can enter cells and mutate your dna, which can cause cancer/birth defects/ reproductive harm
I think the correct answer from the choices listed above is option C. Cells in multicellular organisms differentiate as they continue to divide and increase in size because cells will now perform special functions and have become different to other cells. Hope this answers the question.