Answer:
The correct answer is: With the theory of discontinous development.
Step-by-step explanation:
In developmental psychology, one of the most important questions is whether the individual's development is a continuous or discontinuous process.
The theorist's that argue that development occurs in a continuous manner propose that human development occurs as a gradual process across the life-span, whereas theorist's that believe that development occurs in a discontinuous manner argue that development occurs in stages, where individuals being able to elicit certain behaviors in certain clear and definite stages.
In this particular case, Roger believes his infant daughter is going through very distinct stages of development and is suddenly, upon turning six months old, able to do far more than she could at 5½ months.
This perspective is consistent with the discontinuous approach to development.