The answer is: B. Memory is located in specific sets or circuits of neurons.
After a certain memory is deemed as 'important' for us, they will kept together within neurons as a part of long term memory, in the same pattern that we infer when we experience the memory at the first time.
For this to happen, the memory has to redundantly encoded and retrieved several times, The ability for neurons to held the information become weaker as we got older. This is why elderlies tend to start to forget a lot of things after reaching a certain age.