"To our sister republics south of our border, we offer a special pledge: to convert our good words into good deeds, in a new alliance for progress; to assist free men and free governments in casting off the chains of poverty. But this peaceful revolution of hope cannot become the prey of hostile powers. Let all our neighbors know that we shall join with them to oppose aggression or subversion anywhere in the Americas. And let every other power know that this Hemisphere intends to remain the master of its own house." The bolded sentence in the selection above signifies a shift in tone. Which sentence below best explains Kennedy's tone after the shift? (3 points)

a
He is letting enemies know that they will not be allowed to have an influence in the Americas. His tone is cautionary.

b
He is stating that the United States will support people and governments in the Americas, but cannot pledge to fight enemies outside of the country. His tone is regretful.

c
He is suggesting that other countries are poor. His tone is sorrowful.

d
He is warning other countries that the United States will support peaceful revolutions. His tone is regretful.