Final answer:
Ehrlich was incorrect in postulating that individual cells make many different receptors. B and T lymphocytes of the adaptive immune system indeed create specific receptors, but through recombination that allows vast receptor diversity without requiring separate genes for each specificity.
Step-by-step explanation:
Ehrlich's concept of a selective model of immunology was largely correct; however, the claim that each cell makes many different receptors (A) is not accurate. In Ehrlich's time, the knowledge of how the immune system could potentially make a vast number of different receptors was not fully understood. We now know that during the adaptive immune response, B and T lymphocytes each create a specific antigen receptor through a process that allows a vast diversity of receptors to be produced without requiring an individual gene for each receptor specificity. This is achieved by a recombination process of receptor genes, permitting a tremendous variety of antigen receptors to be generated from a limited genetic material.
In contrast, the innate immune system utilizes a limited set of receptors that are broadly active against many kinds of pathogens, as the specificity and large number of receptors characteristic of the adaptive immune system are not present in innate immune responses. The other options B, C, D are representative of Ehrlich's correct understanding of the immune system including receptors binding to antigens like enzymes bind substrates (B) and the concept of receptor-pathogen interactions leading to inactivation of the pathogen or stimulating the immune cells (C and D).