Answer: The adult stage for one-celled organisms is usually extremely long.
Explanation:
The first one is false, I'm no expert, but I'm pretty sure that there is some yeast that don't produce spores, even in normal conditions.
The third is false, Algae can be unicellular <em>and </em>multicellular.
The fourth is false, All the Algae in the world is close to <em>half</em> of the ogygen in the world.
So that leaves the second, The adult stage is usually long for one-celled organisms.
