Find the mistakes and write down the correct sentences. 1)european explorers crossed the atlantic ocean before the 15th centuty. 2)they knew a lot about the atlantic ocean. 3)columbus saw america for the first time on the 10th of october, 1492. 4)it took him 5 months to cross the atlantic ocean. 5)they had very fast ships. 6)we ctltbrate columbus day on the 14th of october. ( )

1. European explorers had crossed the Atlantic Ocean before the 15th century. (it's true)
2. They knew very little about the Atlantic Ocean. 
3. On the 12th of October, 1492 Columbus saw America for the first time.
4. It took him 2 months to cross the Atlantic Ocean. 
5. They had slow ships.
6. We celebrate Columbus Day on the 9th of October.