I participated in the exercise
Use "persons who participated."
Yes, that is correct grammar.
I have to HAVE it cleaned.I had to HAVE it cleaned.
This should say, The next stop will be somewhere in Vasayas, then it will be correct grammar. Written as it is it is not on correct grammar.
No, it is not correct
No, it's not correct grammar. The correct way to say it is: "was able to confirm"
No, it is not proper grammar. The correct phrasing is "you and I."
No, the correct grammar would be "Look at what you got."
Yes, 'you were correct' is perfect grammar. An example sentence: You were correct when you said that a tomato is a fruit.
Absolutely.
Yes
No, The correct grammar for this sentence would be, "He finished doing his homework."