In complete metamorphosis, the immature stages are called in incomplete metamorphisis, the immature stages are

1. larva, 2. nymph

Explanation:

In complete metamorphosis the precursor of insect undergoes with four distinct stages to develop into complete adult insect. These are egg, larva, pupa and adult.

In incomplete metamorphosis the insect precursor hatches from an egg and then goes through several nymphal stages similar to adult.

Therefore, in complete metamorphosis the immature stage is called as larva and in the incomplete metamorphosis the immature stage is called as nymph.

if your own plato the answer is b. the fern transitioned from sporophyte generation to gametophyte generation.