Final answer:
During the formal operational stage, an adolescent's verbal problem-solving ability is evident in their abstract thinking. They can think logically, deal with abstract ideas and hypothetical situations, and develop new ideas.
Step-by-step explanation:
The abstract quality of thinking during the formal operational stage is evident in an adolescent's verbal problem-solving ability. This stage, according to Piaget's theory of cognitive development, occurs from about age 11 to adulthood. In the formal operational stage, adolescents can think logically and deal with abstract ideas and hypothetical situations. They are capable of using abstract thinking to problem solve, consider multiple points of view, and form new ideas.