Robin Hill discovered that the isolated chloroplasts from plants can release oxygen when they are illuminated by sunlight in the presence of a suitable electron acceptor. This showed:
I. oxygen (${\mathrm{O}}_2$) is produced by a reaction that is separate from carbon dioxide (${\mathrm{CO}}_2$) fixation.
II. the reaction in which oxygen is released requires light.
III. the light dependent reaction of photosynthesis is a result of a series of redox reactions.
1. I and II only
2. I and III only
3. II and III only
4. I, II and III