What did President Kennedy make citizens of the United States feel about
their duty to country?
A. it was their right
B. it was their privilege
C. it was their responsibility
D. it was their calling

It would be C.

Explanation:

His famous Inaugural post " Ask not what your country can do for you, but what you can do for your country." Not only was a warning to the Soviets and their Allies against pushing the US into a nuclear war, but a call to service from the US citizens to do their duty and defend the country, to see the importance of civic action and public service.  This challenged every American to contribute in some way to the public good.

Explanation:

The Columbian Exchange is extremely important on many levels. The primary sphere of relevance is that it marked one of the first moments where there was a pure exchange of ideas, livestock, food, and goods between the world of "the West" and the "New World."