This is the only possible answer because when animals die they might get trapped under layers of bone conserving the bone, and B is the answer because if bones are conserved in the sediment Scientists may be able to recognize certain animals for example, 1000 years ago a cow dies and is buried by sediment, the skeleton remains allowing scientists in the present year to analyze it, they might notice slight changes in things like the bones, or the teeth, etcetera, thus this is how Scientists found proof of evolution.
