Choose the correct form of the 3rd Conditional:
1.If the Titanic (didn't hit / hadn't hit) an iceberg, it (wouldn't have sunk / doesn't sink) .
2.If the Aztecs (had defeated / defeated) Cortes' soldiers, the Spanish (mightn't conquered / mightn't have conquered) Mexico.
3.What (happened /would have happened) if Columbus (thought /had thought) the world was flat?
4.If the Tsar's soldiers (hadn't shot / wouldn't shoot) demonstrating workers in 1905, there (mightn't been / mightn't have been) a revolution in Russia.
5.John Kennedy (couldn't be assassinated / mightn't have been assassinated ) in 1963 if he (hadn't been travelling / hadn't travelling) in an open-top car.