Based on the statement that Fossil A is found closer to the surface compared to Fossil B, the most reasonable conclusion is:
Fossil B is most likely older than Fossil A.
This conclusion is based on the principle of stratigraphy, which holds that in an undisturbed sequence of sedimentary rocks, the oldest layers are at the bottom and the youngest layers are at the top. Therefore, if Fossil A is found closer to the surface, it is likely younger than Fossil B, which is found deeper.