External fertilization occurs in which type of environment?

aquatic

forested

savanna

steppe

Aquatic

Explanation:

In aquatic environments, most of the upper and inferior eukaryons have external reproduction systems, for example, egg lying or free disposal of sperm. This is a common feature on fishes, mollusks, crustaceans, sea-worms, sponges and other lower forms.

It does not count for mammals, having these latest internal systems of reproduction.

All the other environment named, are terrestrial. Where the most majority of the living being had evolved to use internal fecundation.