The rock was once buried under a swamp. Water from a river washed across the rock. The rock was once sediment at the bottom of an ocean. Migrating animals dropped the seashell into the rock.
I am hesitating between 4 options to answer the following question, which option should I choose?
Question: A geologist found several types of seashell fossils in a rock layer. Which is the best conclusion about the rock layer?
Possibilities:
- The rock was once buried under a swamp.
- Water from a river washed across the rock.
- The rock was once sediment at the bottom of an ocean.
- Migrating animals dropped the seashell into the rock.

The rock was once sediment at the bottom of an ocean.