Answer:
The correct answer is A: hard spines on body.
Step-by-step explanation:
Cambrian explosion represents a moment in the history of life in which fauna new shapes appeared showing mineralized exoskeleton. The term "mineralized exoskeleton" refers to a hard structure that supports and protects the body, covering the soft parts. These skeletons are made of minerals that make them harder and more resistant. The development of these structures more rigid and resistant to natural destruction was a huge triumph.
One of the principal characteristics in the Cambrian explosion was then the diversification of organisms that presented plaques, shells, and other hard parts.
Some of the first fossils in appearing are some little skeletal plaques, spines, tubs, and shells. Among these are spicules of some sponges and shells of some brachiopods.