Which one of the following best states the main idea of the passage? A. Differences in the demographics of United States slavery and Russian serfdom can help explain the different kinds of resistance practiced by slaves and serfs in their respective countries. B. Historians have yet to undertake an adequate comparison and contrast of Russian serfdom and United States slavery. C. Revolts by Russian serfs were commonly characterized by collective action. D. A recent study has questioned the value of comparing United States slavery to Russian serfdom, especially in light of the significant demographic and cultural differences between the two countries. E. De Tocqueville failed to recognize the fundamental differences between Russian serfdom and United States slavery which more recent historians have identified.