What does it mean to say the united states operates on an ongoing payment system?

Why did lincoln inform the confederacy that he would not e sending troops or weapons as food supplies were sent to fort sumter?

Ais a group of people living and working under a set of rules and traditions.

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?