User Newell distinguishes between fixed structures and variable content. These ideas are best related to the Pylyshyn's ideas as follows:

a. Variable content refers to cognitively penetrable processes; fixed structures refer to cognitively impenetrable representations

b. Variable content refers to cognitively impenetrable processes; fixed structures refer to cognitively penetrable representations c. Variable content refers to cognitively penetrable representations; fixed structures refer to cognitive impenetrable processes

d. Variable content refers to cognitively impenetrable representations; fixed structures refer to cognitively penetrable processes