We need to see the bar magnet
Answer:
Cytoplasm is the answer
Explanation:
Cytoplasm is a thick solution that fills each cell and is enclosed by the cell membrane. It is mainly composed of water, salts, and proteins. In eukaryotic cells, the cytoplasm includes all of the material inside the cell and outside of the nucleus.
Rbc dont have a nucleus to pack more haemoglobin. it also has a biconcave shape to increase surface area.... idk about the other two. sorry