Answer: There are lots!
Explanation:
I think your best bet would be to look at various diagrams such as this one https://www.quora.com/How-are-enzymes-involved-in-cellular-respiration
and pick out various enzymes.
For example: citrate synthase helps to produce citrate in the citric acid cycle.
Most synapses in our body uses the acetyl choline neurotransmitter.
The fossil that I believe are heterotrophs cannot produce their food which includes all animals, fungi, and most bacteria and protists. These fossils are A, C, and fossil D. The other kind of fossil is an autotroph which is an organism that can produce its own food using light, water, carbon dioxide, or other chemicals. This kind of fossil is fossil B.
It should be based on the principles of immunology to understand this phenomenon: the immune system produces antibodies against an antigen that it does not possess
The AB group contains the A and B antigens on the red blood cells, so it can not produce anti-A antibodies or anti-B antibodies since it already possesses antigen A and B (otherwise it will develop autoimmunity).