You are given a paragraph, a question and some answer options (associated with "A", "B", "C", "D", etc.) You need to list all the correct answer options with their associated letters (e.g. "A" can be a valid answer). Note that sometimes, more than one option can answer the question correctly and completely. In those cases, please generate all such options separated by a comma (e.g. "A, B" is a valid answer). Do not generate anything else apart from one or more of the following characters: 'A', 'B, 'C', 'D', etc.
Example: Paragraph- Sent 1: Obama was born on August 4, 1961, at Kapiʻolani Maternity & Gynecological Hospital in Honolulu, Hawaii.
Sent 2: He is the only President to have been born in Hawaii.
Sent 3: He was born to a white mother and a black father.
Sent 4: His mother, Ann Dunham (1942-1995), was born in Wichita, Kansas, of mostly English descent, with some German, Irish, Scottish, Swiss, and Welsh ancestry. Question: How old was Obama's mother when he was born? (A) teenager (B) in his 40s (C) mid 20s (D) almost twenty.
Example solution: D.
Example explanation: Obama was born in 1961. His mother was born in 1942 and 1961-1942=19. Therefore, "almost twenty" answers the question sufficiently.

Problem: Paragraph- Sent 1: Fossils may form in other ways.
Sent 2: Fossils can be preserved almost completely.
Sent 3: In this process, the organism doesnt change much.
Sent 4: As seen below, tree sap may cover an organism.
Sent 5: With time, the sap hardens.
Sent 6: It turns to into amber.
Sent 7: The original organism is preserved.
Sent 8: This is very exciting for scientists.
Sent 9: They are able to study the DNA of the organism that no longer lives on Earth.
Sent 10: Some animals have been found frozen in ice.
Sent 11: Others have been found in tar pits after falling in.
Sent 12: Molds and casts are another way organisms can be fossilized.
Sent 13: Have you ever walked in soft mud and left footprints?
Sent 14: Once in a while, these traces of organisms can be preserved.
Sent 15: In this case, nothing is left of the organism.
Sent 16: A mold is an imprint of an organism that is preserved in rock.
Sent 17: The organisms remains break down completely.
Sent 18: There is nothing left of the original plant and animal. 
Question: How is a mold of an footprint made? (A) With plaster (B) By gravity (C) An animal or a plant organism breaks down completely and preserved in a rock (D) The footprint is made in a soft substance that is imprinted and preserved as a rock (E) Through erosion (F) Imprint of an organism- walking through mud (G) It just sticks.

Solution: C, D, F.