Which one of the following categories of organisms do not evolve oxygen during photosynthesis?

The photosynthetic bacteria (e.g. purple non-sulphur bacteria) photosynthesise using bacteriochlorophylls $a$ and $b$ in anoxic environments, such as the bottom mud of ponds and other stagnant water, although they are able to survive in air. The reducing agent involved is hydrogen rather than water, so oxygen is not produced. These bacteria efficiently use infrared light for photosynthesis.