Passage The Effects of Gravity Are Effectively Negated If an Object

Passage
The effects of gravity are effectively negated if an object is in free fall.  For example, an object orbiting the Earth experiences an apparent weightlessness known as microgravity.  Because the human body evolved under the influence of Earth's gravity, human physiology undergoes several changes in microgravity environments.  Puffy face syndrome (PFS) occurs when an astronaut's extracellular fluid shifts toward upper body regions, resulting in facial bulging and leg shrinkage.  Elongation of the spinal column also occurs as intervertebral discs (spinal cartilage) decompress, making astronauts up to 6 cm taller.Researchers simulated microgravity-induced spinal elongation on Earth by suspending 50 volunteers by the arms, holding each above the ground in an upright position.  The thickness of each intervertebral disc was measured prior to and following 10 minutes of suspension.  Researchers then compared the percentage change in intervertebral disc thickness to similar measurements recorded in microgravity, as shown in Figure 1.
Figure 1  Percentage change in intervertebral disc thicknessIn theory, spinal elongation would also occur in reduced-gravity environments like the surface of the Moon, where the acceleration of gravity is one-sixth that observed on the Earth's surface.
-Which of the following statements explains the discrepancy between the microgravity data and the laboratory data for the experiment described in the passage?

A) In microgravity, gravitational forces were converted to tension.
B) In the laboratory setting, the weight of the body still acted on spinal cartilage.
C) The mass of the laboratory volunteers did not decrease.
D) Laboratory volunteers were not suspended upside-down to account for PFS.

Correct Answer:

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