Passage Summary: Scientists found a DNA structure inside a plant. This structure has two versions of a certain gene, which is what you would expect to see if the structure was actually the leftover parts of a different organism that the plant swallowed long ago.

Reasoning: The presence of two versions of a gene in a nucleomorph suggests it is the remains of an engulfed organism, as a single version would be expected otherwise.

Analysis: This 'Most Strongly Supported' question requires us to synthesize the provided facts. We are told that endosymbiosis involves one organism engulfing another and that the presence of two gene versions is a key indicator of this process. Since the chlorarachniophyte's nucleomorph contains these two versions, the most logical inference is that this plant is an example of an organism that originated through endosymbiosis. Look for an answer that connects the specific evidence found in the plant to the general definition of endosymbiosis provided at the start.