1) The fall of the Berlin Wall in 1989 symbolized the end of the Cold War and the reunification of East and West Germany.

2) The word "triangle" contains four vowels: I, A, E, and E.

3) The first commercially available digital camera, the Dycam Model 1, was introduced in 1990 and had a resolution of 376 x 240 pixels.

4) In Norse mythology, Valhalla is a majestic hall located in Asgard, the realm of the gods. It is the afterlife destination for brave warriors who die in battle, where they are greeted by the Valkyries and engage in feasting, drinking, and preparing for the final battle of Ragnarok.