Which was a reason for the development of trench warfare on the western front during wwi

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.

The enforcement clause of the fourteenth amendment states what congress had the authority to a. grant citizenship to people b. change the constitution c. enforce only the bill of rights d. make laws to apply the amendment

Why did china build the great wall of china?