Answer:
C) first appearance of most invertebrates.
Explanation:
The Cambrian Explosion occurred 542 mya. The earliest complex animals arose in the sea at the beginning of the Cambrian Explosion. It would take another half a billion years for mammals to rise. Multicellular life dates back 1.2 bya, but more cpomplex life, such as animals, did not occur until the Cambrian Explosion. In the beginning of the Cambrian Explosion, many soft-bodied animals, such as jellyfish and sea anemones appeared.
