Axon: the messenger cell that carries the command to contract muscles.
I believe the answer is A!
All mentioned complexes (receptor-hormone, antibody-antigen, enzyme-substate) are involved in a molecular recognition.The molecular recognition involves <span>non-covalent </span> interaction between molecules. To form complex, molecules must be complementary in shape and charges, and usually, they are compared to key and lock. This way, the selectivity and specificity of recognition between molecules are assured.
<span>If you look at hominids' mouths you can learn a lot. You can compare the teeth to see what they eat. Different foods cause a different amount and type of wear. You can also point out individuals by matching their teeth with what you know about them.</span>