**Core Concept**
X-rays are a form of electromagnetic radiation used in medical imaging to visualize internal structures. The modification of X-rays refers to the process of altering their properties to enhance image quality or reduce radiation exposure.

**Why the Correct Answer is Right**
The correct answer is related to the concept of beam hardening, which occurs when low-energy X-rays are absorbed by the body, leaving only higher-energy X-rays to reach the detector. This results in a loss of contrast and a harder X-ray beam. To counteract this effect, X-rays are often modified by filtering them through a material such as aluminum or copper, which absorbs low-energy X-rays and allows only the higher-energy X-rays to pass through.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because beam hardening is the primary reason for modifying X-rays, not the other way around.
**Option B:** This option is incorrect because X-rays are not typically modified by changing their frequency or wavelength.
**Option C:** This option is incorrect because modifying X-rays is not primarily done to reduce radiation exposure, although it can be a secondary benefit.

**Clinical Pearl / High-Yield Fact**
To remember the concept of beam hardening, recall that "hard" X-rays have higher energy and are less absorbed by the body, resulting in a loss of contrast. This can be countered by filtering X-rays through a material that absorbs low-energy X-rays.

**Correct Answer:** B. X-rays are modified by filtering them to reduce beam hardening.