In order to place fish into a major group, the biologist need to look at the structure and composition of the skeleton and the structure and arrangement of the fins
Option B
Step-by-step explanation:
The skeleton composition and structure categorizes the fish into major groups. The two major groups of category of fish are cartilaginous fish and bony fish. The composition and structure of skeleton tells about the unknown fish to whether to have a skeleton of cartilage or of bones, either of the two will make it fall into one of the category.
The arrangement of fins further let them substantiate the fact of being either of the two categories of fish based on their bony fin rays or not. It is known that fins except for caudal fins appear in pairs and their arrangement tells about its category.