Identify which of the following organisms are monoecious and which are dioecious:
$(a)$ Earthworm ........... $(b)$ Chara ...........
$(c)$ Marchantia ........... $(d)$ Cockroach ...........

(A) Earthworm: Monoecious (Hermaphrodite).
$(b)$ Chara: Monoecious (Both male and female sex organs are present on the same plant).
$(c)$ Marchantia: Dioecious (Male and female sex organs are present on different thalli).
$(d)$ Cockroach: Dioecious (Male and female individuals are separate).