Collimation reduces the beam size to the patient to 2.75 inches.

• A. Increases beam size
• B. Changes beam energy
• C. Increases energy
• D. Reduces the beam size to the patient to 2.75 inches

Answer: (D)

Collimation shapes the X-ray field by adjusting the aperture of the beam, determining the cross-sectional area that reaches the patient. Saying the beam is reduced to 2.75 inches describes this field-size control—the collimator narrows the beam to a specific, smaller diameter to limit exposure and scatter. It does not change the photons’ energy; beam energy is set by kVp and filtration, not by collimation. So the other ideas—making the beam larger or increasing energy—don’t fit, because collimation’s role is to control field size, not energy.