Final answer:
Improper biomechanical motion between two vertebrae is best referred to as C. subluxation.
Step-by-step explanation:
When two vertebrae are misaligned or have lost their normal movement, it can lead to subluxation. This can occur due to factors such as injury, poor posture, or degenerative changes in the spine.
For example, if there is a misalignment or abnormal movement between the fourth and fifth vertebrae of the spine, it would be referred to as a subluxation.
In conclusion, when there is improper biomechanical motion between two vertebrae, it is best described as subluxation. The correct answer is C. subluxation.