What determines a blood type to be "O"

the type of surface protein.

Explanation:

On the exterior portion are trans-membrane glycoproteins are sugar residues with specific orientations that give rise to blood types. The sugar residue prevents people with different red cells from mixing.

Type O has no antigen b/c no sugar disposition - doesn't look any different to the immune system. Has antibodies against both A and B; has no antigens which means have both antibodies

because health skills are tools and strategies and also practical skills are also something you need to learn (like tools and strategies) and put it in reality.