Answer
You could test the hypothesis by looking for things which were shared between the green algae and the land plants but not by other organisms, especially not other photosynthetic organisms: oxygen production by photosynthesis and green chloroplasts with two outer membranes.
Work Step by Step
This hypothesis needs to be connected to the idea of related organisms sharing similarities. Then it’s just a matter of scanning this and other chapters for basic features of green algae and of land plants which are shared.
