Which of the following tests would help differentiate primary polycythemia from secondary polycythemia?

When a person falls from a significant height and lands on his or her feet, axial loading results in:

A) compression or burst fractures to the lumbar spine. B) shearing injuries to the liver, spleen, and aorta. C) crushing injuries to the heels and hip dislocations. D) disc injuries to the lower cervical and upper thoracic spine.

What is the preferred target-surface distance when using the paralleling technique?

What will be an ideal response?