Fast, наверно. Class и Grass - имена существительные.
What would you do If you lose a lot of money?
Where would you go if you finish your homework earlier?
When would you meet friends If you go to the park later?
...
Who is playing football with his friends?
What is he doing with his friends?
What game is he playing with his friends?
Who he is playing football with?
The customer is always right, because he/she pays money.
A lot of types of people in our world and every persone who offers different services must be ready for cruel/bad/nasty/<span>naughty people, because he/she decided to work in this </span>sphere and that did it on their own.