Answer:
If this is wrong im very sry, but i belive the answer is white blood cells
Explanation:
These are the cells that fight off infections and bactieria that is not sopposed to be in the human body, or any other living creature.
The answer is B.
I think its safe to assume we all have had a cup of ice water. The ice always floats at the surface of the water.
Khan Academy is great! Also, Alison (it's a website) has some free courses as well.