All of the choices are correct
Because it was mainly Europe that was Christian. Asia was for example mostly Buddhist, Confucian, and Hindu. The Middle East and Northern Africa was Islamic. The rest of the world was influenced by Europe and it’s Christianity.
Trench Warfare was a form of military conflict in which opposing sides fought one another from trenches facing one another. WW1 warfare introduced the first large-scale use of chemical weapons as well as bringing in airplanes and tanks for the first time.
The answer would be the 2nd option.