Fighting conducted from a system of ditches protected by barbed wire

trench warfare

Explanation:

The World War I was mostly fought in the manner of the trench warfare type. Even though there were multiple new inventions that were used in the war, such as the poisonous gas, mustard gas, chlorine, submarines, the first military planes, still the trench warfare was the dominant one. Basically, this warfare was lead in a manner where there were long systems of ditches that were deep enough to protect the soldiers from the artillery, barbed with wire to stop the enemy and give time to the soldiers to react. While in a way the soldiers were protected from some things, and they were able to shoot and hide, there were also very bad sides of this warfare. Whenever a bomb fell into the ditches, there where always lot of casualties, as they were trapped inside with it. Also, the whenever there was rain, the ditches were filling up with water to a certain level, making them muddy, or even like little canals, where the soldiers were getting sick very easily.

b. sec, foreign relations

number 1 is a)