Answer:
A- Casts
Step-by-step explanation:
Tarpits fossils preserve things and don't let them harden. Tar is a sticky, slimy substance so it doesn't form from hardened sediment.
Carbon films, I don't really need to explain this one, but I will, for you. Carbon film fossils are thin, almost 2-d. Carbon films come mainly from leaves, and are moldable; Although I'm sure you don't want to risk breaking a million-year-old fossil! The Carbon film is not from sediment, as it is from carbon.
Amber fossils come from sap, which is not sediment, merely tree "blood"
Cast fossils come from a sediment impression or an imprint
Therefore, by process of cross-referencing, elimination, explanation, and evidence, we can safely say that cast fossils form from hardening sediment.
Also sorry about the little red line in the middle of the photo, downloading complications