IELTS Grammar: 'overview' mistakes

 Here are some sentences that people wrote below Thursday's writing task 1 lesson. Can you find and correct the mistakes?

1. There are a lot of fluctuations in cost these years.
2. Prices of both food and oil have a significant increase in eleven years.
3. The trends show almost similar figures throughout the period.
4. Oil and food prices follow nearly same trends within period.
5. Both goods increased theirs prices throughout the period shown.
6. Both goods had their prices increased throughout the period shown.