OPTIONS:
(1). Plant reproduction.
(2). sub-units of species.
(3). gastropod shells.
(4). an individual mature sponge.
(5). Microscopic organisms.
(6). members of their own species.
(7). peachleaf willow.
(8). seed dispersal.

You are presented with the quiz "What produces both eggs and sperm?" But you don't know the answer, so you turn to your teacher to ask for hints. He says that "adult sponges produce eggs and sperm" and "an adult is mature, fully developed". So, what's the best answer to the question?
Answer:
(4).