Final answer:
The correct infinitives in the given sentences are 'saber', 'tocar' and 'ser'.
Step-by-step explanation:
The correct infinitives in the given sentence options are:
- saber
- tocar
- ser
So, the complete sentences would be:
- Mi hermana sabe tocar muy bien.
- Eres muy bueno para tocar la orquesta.
Here, the infinitives 'tocar' and 'ser' are used correctly in the given context.
Learn more about Spanish infinitives