Fossil B belongs to the same period as the trilobite.
Explanation:
If we look at the image and the organism key, we can see that fossil B and the trilobite are in the same layer of the rock. This means that they were from the same time period. If something is found at a deeper layer in the rock (or the bottom of the chart) it means it is older than something found above it. Likewise, if something is on the outside layer of the rock (or the top of the chart) it is younger than something found below it.
