Which languages can Yvette understand?

The correct option states that Yvette can understand four languages, including German and French. This indication suggests that her language proficiency spans beyond just two specific languages, which would encompass a broader capability that includes English and perhaps other languages as well.

Understanding multiple languages allows for greater communication skills, and mentioning German and French specifically highlights that these are two of the languages she can comprehend. Given that the question emphasizes the number of languages she can understand, the selection of the option that notes her ability to understand four languages aligns precisely with the implied depth of her linguistic skills.

Other options limit her proficiency to either two languages or only specific pairs, which does not reflect the breadth that option C describes. Therefore, the correct answer effectively communicates her diverse language understanding.