Of these quotations, the only one that (in my view) specifically supports democracy or democratic ideals is speaker A.
John Locke, from whose writings speaker A's quote is drawn, is the philosopher most often identified as expressing the theoretical underpinnings of British and American democracy. This statement was largely paraphrased by Thomas Jefferson almost a century later in the Declaration of Independence. The essence of democracy can be defined as the principle that governments obtain their power from the consent of the governed, as is the case (however imperfectly) in the UK and the US.
The quote from speaker B, drawn from the work of Niccolo Machiavelli, might be viewed as the antithesis of democracy. Machiavelli, however, in The Prince was not so much stating a political philosophy as describing what autocratic leaders—kings and princes—have historically done in order to stay in power. So, the "precepts" of The Prince are by definition irrelevant to democratic thinking (though the work itself, concerned with the discussion of political power, is not).
Speaker C is referring more to the economic ideal of capitalism than to political democracy. We can see from the example of present-day China that capitalism and authoritarianism are not mutually exclusive, since China has what is essentially a free-enterprise system under a non-democratic government.
Finally, speaker D in some ways suggests the opposite of democracy, seeming to deny that the will of the majority has any validity as a basis of government. However, unless we see the context of the statement, it's difficult to see the overall implications of the idea that the individual—and not the "majority"—creates progress.
The quote could easily come from the writings of Ayn Rand, whose principal ideas revolve around laissez-faire capitalism (often associated with democracy, though not inherent to it) as the only valid economic system. Yet Rand's social and political thinking—which suggests that a caste system in which elites rule the "lesser " members of the populace is ideal—is the opposite of democracy.