"According to the passage, each of the following statements concerning ancient Greek juries is true EXCEPT:"
This is an "except" question, so A is the right answer because it is not supported by the passage. It is right because it is wrong, if I am understanding your question correctly.
Take a look at line 33: "True, in Athens the juries were representative of a broad spectrum of the population, and these juries, drawn from diverse social classes, both interpreted what they had heard and determined matters of fact."
This sentence explains why C is true and why A is not true. It never says that juries were composed "largely of people from the lowest classes." This implies that the jury was mostly made up of poor people, which was not the case. The jury was representative of the population as a whole. This is why A is not supported by the passage, and is our correct answer.
