Mark the consequence if it is intentional.
a.
europeans take corn to africa. corn becomes an important crop there.
b.
some sailors and conquistadors have smallpox. they come in contact with native americans who contract the disease and die after infecting their relatives and neighbors.
c.
affluent europeans buy sugar from merchants in european cities. millions of people in africa are kidnapped by african slave traders and sold to european sugarcane planters in the caribbean.

Martha participates in a research study in order to receive extra credit for her psychology class. when she arrives in the research office she is given a can of what looks and tastes like beer, but which actually contains no alcohol. in the adjoining room martha's classmate karen is also participating in the study. karen receives a can of alcoholic beer. if the experiment was designed to test the effects of alcohol on concentration, then who is exposed to the independent variable?