Which of the following is an example of hard power?

(a) the united states sent aid to victims of the 2005 tsunami in southeast asia.
(b) the united states enforced trade sanctions with north korea.
(c) a group of american filmmakers organized a film festival in venezuela and offered winners the chance to study for one year in the united states.
(d) the new york philharmonic orchestra traveled to north korea in february 2008 to perform a series of concerts and participate in workshops with north korean musicians.