Answer:
A. Smallest
Step-by-step explanation:
The term "runt" refers to the smallest and weakest member of a litter of animals, such as puppies in this case. The runt is typically smaller in size compared to its siblings and may face challenges in competing for resources like food and attention. So, the correct option is "A. Smallest" because the runt is characterized by being the smallest or least physically developed member of the litter.