What does it mean to "buy on margin?" What are the advantages? What are the disadvantages

The letter explains the treatment of prisoners of war. of 3.6 million prisoners of war, only several hundred thousand are still able to work fully. a large part of them has starved, or died, because of the hazards of the weather. . the camp commanders have forbidden the civilian population to put food at the disposal of the prisoners, and they have rather let them starve to death. –letter to defendant wilhelm keitel from alfred rosenberg the letter prosecutors at the nuremberg trials prove that soviet prisoners were a) treated well despite the conditions. b) treated poorly. c) subject to execution. d) subject to crimes against peace.