Answer:
A. They have been genetically modified to grow fatter.
Explanation:
Chickens raised for meat production have been selectively bred over the years to grow faster and produce more meat. This selective breeding has focused on traits like rapid growth and increased muscle mass, often at the expense of other factors like skeletal development. As a result, many of today's chickens grow so quickly that their bodies struggle to support their weight, leading to skeletal and musculoskeletal issues that can make walking difficult or painful. This phenomenon is sometimes referred to as "fast growth syndrome" or "rapid growth syndrome" in poultry farming.