In a research study, one set of subjects received a treatment and another set of subjects received a placebo. This research study is an example of a(n):

explanation:

with the profits from the european sales, merchants purchased europe's manufactured  goods, including tools and weapons. then the merchants shipped those manufactured  goods, along with the  american  sugar and rum, to west africa where they were bartered for  slaves.

haile selassie i was the emperor of ethiopia from 1930-1974

answer; lorenz;