Final answer:
Layers that are adjacent, like Layers 8 and 9, are closest in age and likely to contain similar fossils due to their short span of time separating their formation.
Step-by-step explanation:
The layers of rock that are closest to each other in position will usually be the closest in age and have similarly structured fossils. Since rock layers form sequentially with newer layers on top of older ones, adjacent layers will have been deposited during relatively similar time periods. This proximity in deposition times means that the fossils found within these adjacent layers will likely be close in terms of structure and age. Option B, Layers 8 and 9, would be most likely to contain the closest related fossils because they are contiguous; one layer is right above the other, indicating a shorter span of time separating their formation as opposed to more distant layers.