_______, the little bird chooses a hollow tree for a nest and seals herself in until her chicks are grown.

Intermediate  B1 : Ability to make simple conversations about familiar topics. At B1 level, you can describe experiences, events, and deal with many situations while traveling.
Advanced  C1: Ability to express yourself fluently in almost any situation, without the need to search for expressions. You are able to perform complex tasks related to work and study. You can also produce clear, detailed texts on challenging subjects.