Final answer:
The sentence that represents the main idea is sentence #3: 'A passionate socialist, Keller crusaded against class distinctions.'
Step-by-step explanation:
The sentence that represents the main idea is sentence #3: 'A passionate socialist, Keller crusaded against class distinctions.'
This sentence introduces the main idea of Helen Keller's activism and her fight against social classes. It is the central focus of the passage and provides a theme that connects the other sentences in the text.
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