Why would people buy stocks "on margin " if it was so risky?

Look at the graph. where p is price and q is quantity, what might cause a move from b to a?

Name at least three countries neaolpeon controlled

The u.s. government has three branches: executive, judicial, and legislative. each branch plays a different role in making sure laws are passed, enforced, and applied fairly in accordance with the united states constitution. which idea does this scenario best represent?