Which of the following best describes american troops who fought in the mexican-american war?
a. immigrant workers
b. enslaved workers
c. career soldiers
d. volunteer soldiers

The best description regarding troops who fought in the Mexican-American War would be "D. volunteer soldiers," since this was during a time of great patriotic fervor in the United States, due in part to Manifest Destiny. 

Protecting and assisting  u.s. citizens  living or traveling abroad; assisting u.s.  businesses  in the international marketplace; coordinating and providing support for international activities of other u.s. agencies (local, state, or federal government), official visits overseas and at home, and other diplomatic efforts.keeping the public informed about u.s. foreign policy and relations with other countries and providing feedback from the public to administration officials.providing  automobile registration  for non-diplomatic staff vehicles and the vehicles of diplomats of foreign countries having  diplomatic immunity  in the united states