Final answer:
The central hollowed-out area in the shaft of a long bone is the medullary cavity. It is filled with yellow marrow and lined by the endosteum, whereas other structures like the epiphyseal plate and periosteum serve different roles. Therefore, the correct option is 1.
Step-by-step explanation:
The medullary cavity is the central hollowed-out area in the shaft of a long bone. This cavity is filled with yellow marrow and runs the length of the diaphysis, which is the tubular shaft between the proximal and distal ends of the bone. The walls of the diaphysis are made up of compact bone. Therefore, the correct answer to the question is: 1) Medullary cavity.
The other options mentioned such as the epiphyseal plate, periosteum, and endosteum are also parts of the long bone but serve different functions. The epiphyseal plate is involved in bone growth, the periosteum covers the outer surface of bone, providing nourishment and attachment points for tendons and ligaments, and the endosteum is the inner lining of the medullary cavity where bone growth, repair, and remodeling occur.