Answer:
Letter D.
Step-by-step explanation:
TTo determine the change in dietary habits of horses, the best approach from the ones presented is to compare dental features. Teeth can give different pieces of information. The structure of teeth makes it possible to find traces of the food eaten. The same structure also gives information about the food eaten thanks to the shape and borders of teeth.
Studying the diet of modern horses only gives information of the present.
Comparing teeth of horses and donkeys also focuses on the present only. In addition, it adds an element not related to the research (donkeys).
Studying the whole anatomy of a modern horse gives too much information, and all of it about the modern horse only.