which of the following is dioecious ? 
1 . pheretima 
2. hirudinaria 
3 . wuchereria 
4 . hydra

dear student. 
pheretima (earthworm) and hirudinaria (common leech) both are hermaphrodite/ monoecious.
wuchereria (filarial worm) is dioecious. both male and female are separate identities. 
In hydra individuals could be either monoecious or dioecious.

Regards