Rose,
It wouldnt also hurt to mention Interfaces/Classes which carry out that decision. for example, you can say, because of so and so requirement of the system, my <<NamedService>> uses this mechanism to fulfil the needs rather than that mechanism as it had the following advantages..and you can list the advantages, if any. That way, you would also list the requirements of the system and your approach in fulfilling them.
Whats strange is that they do not have mark allocations for Part III essay exam. Even if they had,say 10 marks, allocated to it, that would have helped in understanding their requirements for part III. As is, we are going to list our assumptions, decisions in the part II accompaning document..part III just seems to be a recollection of part II document.
Parag