Which of the following body parts is most likely to be affected by nuclear radiation during the early stages of exposure?

Bone marrow is most affected in the early stages of nuclear radiation exposure because its rapidly dividing cells are highly radiosensitive.

The skin shows burns and later damage but is not the first internal tissue to fail.

Bones themselves are relatively resistant compared with the marrow inside them.

With a clearly most-affected tissue present, denying any answer does not hold.

Marrow damage cripples the production of blood cells, lowering immunity and clotting.

This is why radiation sickness first shows as falling blood counts.