Fig. 25.11 shows three groups of animals, the Sponges, the Cnidarians, and the Bliateria (all other phyla shown in that figure), which all diversified, so in some sense each had an explosion. That would make the Cambrian Explosion three explosions.
Work Step by Step
Since the question asks about three explosions, look for three obvious groups in Fig. 25.11 which could be thought of as each undergoing an explosive diversification.