A. People have different memory capabilities and so make different errors.
B. People have different verbal abilities and vocabularies and so would report their memory differently, even though their actual memory were the same.
C. Peoples have different motivations and so will not all equally hard; they will report exactly what occurred, but they will leave different parts out.
D. People have different past experiences, values and goals and so will experience different events, even when the external event in the same.