The answer is C) in warm, shallow seas.
About 500 million years ago, many multicellular organisms lived in
the seas. It was a rich life in shallow, warm, and continental
seas. The climate was favorable. Reef-forming corals, as well as the first true
vertebrates, some fish, appeared. Trilobites were diverse and
rich. The name trilobite means three lobes in which their body is divided. They lived in warm shallow seas. They avoided a great extinction of species in that time before they were covered by sediment.
