Final answer:
The correct answer to the question, which element was similar between Vietnam and China, is option 'b. Vietnam had strong central governments.' as both nations had periods with strong central governments.
Step-by-step explanation:
The question concerns the differences between Vietnam and China in various aspects. With the given options, the one aspect that was not a distinguishing factor between Vietnam and China was the presence of strong central governments. Unlike the assertion in option a, the scholar-gentry in Vietnam did not owe allegiance to peasants, but were part of a social hierarchy. Option c, which states that Vietnamese women had greater independence, is true as Southeast Asian communities, including Vietnam, did afford women higher status compared to their Chinese counterparts. As for option d, the nuclear family was indeed more prominent in Vietnam compared to the emphasis on extended families and clans in China. Therefore, the correct answer to the question - which element was similar between Vietnam and China - is 'b. Vietnam had strong central governments.', as both Vietnam and China experienced periods of strong centralized rule at different times in history.