Give an example of a key historical event and how it changed history?

The fall of the Berlin Wall/end of the Cold War

Explanation:

On November 9, 1989, as the Cold War began to thaw across Eastern Europe, the spokesman for East Berlin’s Communist Party announced a change in his city’s relations with the West. Starting at midnight that day, he said, citizens of the GDR were free to cross the country’s borders. East and West Berliners flocked to the wall, drinking beer and champagne and chanting “Tor auf!” (“Open the gate!”). At midnight, they flooded through the checkpoints.

More than 2 million people from East Berlin visited West Berlin that weekend to participate in a celebration that was, one journalist wrote, “the greatest street party in the history of the world.” People used hammers and picks to knock away chunks of the wall–they became known as “mauerspechte,” or “wall woodpeckers”—while cranes and bulldozers pulled down section after section. Soon the wall was gone and Berlin was united for the first time since 1945. “Only today,” one Berliner spray-painted on a piece of the wall, “is the war really over.”

cite:  https://www.history.com/topics/cold-war/berlin-wall

c. mass = force / accellaration

step-by-step explanation:

the answer should be monarchy