Not to sure what it could be

no.2

Explanation:

Knock Knock May I come in?

ww1 weapons: tank. tanks were used for the first time in the first world war at the battle of the somme. they were developed to cope with the conditions on the western front. the first tank was called 'little willie' and needed a crew of 3.

a widespread disease that killed many people

the split of the christian church

invasion from arab muslims