Answer:
A). Naturalistic observation.
Explanation:
'Naturalistic Observation' is exemplified as the kind of observation that is primarily inclined towards observing or examining the subjects of research in its natural instinctive environment instead of observing them in a scientifically manipulated environment. The chief objective of such an observation is to assess the behavior n natural conditions and make conclusions accordingly.
As per the question, Dr. Littman's research exemplifies a 'naturalistic observation' as he observes and assesses the subject i.e. 'mothers and toddlers' in their natural environment('how they interact throughout the day') in order to reach a more naturalistic and factual conclusion. Therefore, option A is the correct answer.