How did people on the home front use liberty bonds to support the world war 1 effort?

Which events are correlated but do not necessarily have a causal relationship?

Following archduke franz ferdinand's assassination, austro-hungarian leaders: a. aided the ottoman empire in its campaign to keep serbia under its control. b. executed nearly all prominent serbs living in austria-hungary c. threatened to invade serbia if serb leaders did not agree to a set of strict demands. d.. formed an alliance with great britain to protect austria-hungary from future attacks.

What is the difference between an independent and a dependent variable?