What are marks left in rocks of once-living organisms called?

Ibelieve the answer is c. 

It usually has to be the answer 20

Afemale  with a mutation in one copy of a gene on the  x  chromosome is said to be a carrier for an  x-linked condition. a  male  with a mutation in a gene on the  x  chromosome is typically affected with the  condition.  x-linked recessive diseases  can occur in both  males  and  females. hope this !