What are the options they giving?
Agree. because it is a right
1. b. you use queria because if you say "quise" it means you stopped wanting to learn ballet sometime in the past.
2. b. you use conoci' because you've already met the professor in the past
Ustedes is formal and should be used when talking to someone you’re not so familiar with, like a stranger, or someone that should be addressed with respect, like an elderly person.