One of the Main Factors That Distinguishes the Cambrian Explosion

One of the main factors that distinguishes the Cambrian explosion from all others is that

A) evolutionarily, it was the most recent explosion.
B) many new major groups of animals appeared at this time in contrast to other explosions.
C) it was the time when the dinosaurs became extinct.
D) there was a dramatic drop in species diversity, especially among marine organisms.
E) it was a time of massive volcanic eruptions.