Denzel, a 46-year-old man, is working with his physical therapist on a set of back exercises. Around four weeks ago, Denzel was helping a friend move and attempted to lift a heavy box. Since that incident, he has had severe pain in his lower back that extends into his lower leg. His health care provider prescribed physical therapy three times per week to treat the condition. What happens to cause this condition?      a. Ligaments surrounding the spinal joints have torn due to traumatic injury.           b. The intervertebral disk has shifted out of place, putting pressure on the spinal nerve.           c. Decreased bone density has caused weakening of the vertebra, resulting in a fracture.           d. Crystals of uric acid have deposited within the spinal joints