Answer: A. low degree of substitutability.
Step-by-step explanation:
Substitutability refers to the availability of alternative options to the variable in question. If something is said to be highly substitutable or to have a high degree of substitutability, then that means that it is easily replaceable because it has alternatives. The reverse holds true.
Therefore, Jamie can be said to have a low degree of substitutability because the client wants to deal with only him and if he is removed or unavailable, the company would not be able to deal with the client.