Which one of the following groups of animals is bilaterally symmetrical and triploblastic?

Sponges are mostly asymmetrical and have a cellular level of organisation without true germ layers.
Coelenterates and ctenophores are radially symmetrical and diploblastic (two germ layers, ectoderm and endoderm).
Aschelminthes (round worms) are bilaterally symmetrical, triploblastic and pseudocoelomate animals with an organ-system level of organisation.
Hence the group that is bilaterally symmetrical and triploblastic is Aschelminthes.