The best and most correct answer among the choices provided by your question is the second choice which is "railroad tracks."
<span>By 1860 the Midwest and the East were united by a network of railroad tracks.</span>
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he believed himself to be the first to discover a genuine "science of politics."
I have to say B. The rest were concepts made in Greece, by Greek philosophers, politicians, or mathematicians. An example for an advancement in math is the Pythagorean Theorem. I hope this helps!
