The right answer would be d.It reminds him of the jellyfish that inhabit the waters of Puerto Rico.
Jellyfish, in Spanish is said Agua Viva. Alfredo thought that the sculpture was very similar to a jellyfish, so he reminded of these animals from the waters of his homeland, Puerto Rico. The jellyfish which he way building represented everything in his reality, as doing things with iron was his only interest and he had no friends or family, being immersed in his own world.