Which of the Following Reasons Is Given in the Textbook

Which of the following reasons is given in the textbook to help explain the quick spread of democracy around the world in the late twentieth and early twenty-first centuries?

A) Democracy tends to be associated with competitive capitalism in the economic system, which holds the promise of raising people's standard of living.
B) The economic situation of emerging third-world countries changed rapidly due to the expansion of transnational corporations that offered a democratic example for the peoples of those states to follow.
C) The rising number of American students who studied abroad carried ideas of American democracy to the rest of the world.
D) The increasing prevalence of natural disasters around the globe allowed the Western democracies to demonstrate the benefits of their systems through humanitarian missions in the third world.