Context: This picture shows a fossil of an ancient animal called Asterotrygon. The fossil preserves the shape of Asterotrygon's body.
Asterotrygon was a type of fish. It lived in lakes and gave birth to live young.
Which trait did Asterotrygon have? Select the trait you can observe on the fossil.
A. a wide tail fin
B. spots on its skin
C. a long, thin tail
D. four legs
Select the correct answer from the provided options and reply with the letter associated with it.

C