Answer: Layer 5
Explanation:
The beavers are the species that lived at the time that when they formed fossil they attained the layer number 6.
The other animals or plant species that lived at that time will be found close to the layer number 6.
The layer close to layer 6 is number 5, so the species that lived at the same time as the beavers species will be here only.
Hence, the correct answer is option C