READING problem in "The Cambrian Explosion" ?

"Many of the major phyla of animals arose during the Cambrian period , in what is called the
Cambrian Explosion. Prior to the Cambrian period ,simple one-celled organisms had slowly envolved into primitive multicellular creatures.Then, in a relatively rapid explosion during the period from 540 million years ago to 500 million years ago , there was a period of astonishing diversification in which quickly developing organisms became widely distributed and formed complex communities."

It can be inferred from paragraph 1 that ?
A.some major phyla developed during periods other than the Cambrian period.
B.Many other phyla of animals became extinct during the Cambrian Explosion.
C.descriptions of various animal phyla were created during the Cambrian period.
D.The major phyla of animals that came about during the Cambrian period died out
in the Cambrian Explosion.

What is the correct choice ?Can anyone explain it to me ?
Thanks so much.