Final answer:
During spinal extension, anterior structures are stretched and the disc material moves posteriors, which is most accurately described by option C.
Step-by-step explanation:
The event that is most likely to occur during spinal extension is C. Anterior structures are stretched and disc material moves posteriorly. During spinal extension, a posterior-directed motion of the vertebral column is performed, which includes the straightening from a flexed position or bending backward. This movement elongates or stretches anterior structures, such as the abdominal muscles and the anterior longitudinal ligament, while the nucleus pulposus within the intervertebral disc gets pushed toward the posterior side of the disc space.
In extension, pressure on the anterior portion of the disc decreases, while increased pressure on the posterior portion can push the disc material backward. If the posterior annulus fibrosus is weak or injured, this could potentially lead to issues like disc protrusion or herniation, though typically this risk is associated with flexion movements, especially when combined with twisting or lifting.