The correct responses to the question "Est-ce qu'il y a un ordinateur dans ta classe?" are:
- Oui, il y a un ordinateur dans ma classe. (This is the correct form.)
- Oui, il y a un ordinateur dans ma classe. (This is a repeat but also correct.)
The other responses with "il a" instead of "il y a" are incorrect, as "il a" means "he has" instead of "there is." Additionally, the responses that omit "un" (the indefinite article) are also incorrect.