Final answer:
The piglets followed Sarah because they imprinted on her, which is a biological phenomenon where young animals bond with the first mover they interact with after birth, associating them with safety and nourishment.
Step-by-step explanation:
The scenario described where piglets began to follow Sarah around after she assisted in their birth and took care of them is best explained by A. The piglets imprinted on Sarah. Imprinting is a form of learning where very young animals establish a strong bond with the first moving being they interact with. This behavior increases their chances of survival as they stay close to a caregiver for protection and sustenance. The attachment of ducklings to their mother, or in some cases to a human if they see them first, is a classic example of this biological phenomenon. Similarly, the piglets followed Sarah, associating her with safety and food, in the absence of their natural mother.