Answer:
a. Formal operational
Step-by-step explanation:
Formal operational stage: In psychology, the term "formal operational stage" is described as the last and the fourth stage in the cognitive development theory which was discovered by Jean Piaget. This stage starts from the twelve years and lasts through adulthood period of an individual's life. During this stage, an individual's thinking pattern becomes a lot more advanced and sophisticated. However, an individual tends to manipulate different ideas and thinks abstractly.
In the question above, Davina is in the formal operational stage.