Which substance provides humans with their main energy source

Which element provides strength to the exoskeleton of clams and oysters

Most of the carbon on earth is stored in the form of

The ancestors of plants that lived in water had plenty of water for the young. angiosperms are a group of land plants that evolved a reproductive trait for living on land. this trait protect young plants by allowing them to grow only when water is present and the conditions for healthy development are right. what trait most likely young angiosperms in this way?