How effective was jimmy carter in applying the human-rights principles to american foreign policy? how did his approach differ from the actions taken by ronald reagan?

Carter's foreign human rights policy did not have great record. Given that he supported arming Iran during his administration which has been well known to violate human rights and even seeking favorable position with China whom was known to abused human rights as well. This was not too different with reagan's policy. Where he has established focus on US position on the cold war, through working with the surrounding nations which were not in favor of human rights as well.

The answer to your question would be b