**Core Concept**
The question pertains to the resolution of imaging techniques used in medical practice. Resolution refers to the ability of an imaging modality to produce clear, detailed images of internal structures. Different imaging methods have varying levels of resolution, with some being more effective than others in visualizing small details.

**Why the Correct Answer is Right**
The correct answer reflects the general hierarchy of imaging modalities from lowest to highest resolution. This hierarchy is based on the physical principles underlying each imaging technique. For instance, plain radiography (X-rays) has limited resolution due to the lower energy of the X-ray photons and the scattering of photons as they interact with tissues. Conversely, high-resolution MRI (Magnetic Resonance Imaging) and CT (Computed Tomography) scans offer superior resolution due to the use of high-energy magnetic fields and X-rays, which allow for more detailed visualization of internal structures.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it represents an imaging modality that is not typically associated with low resolution. However, without knowing the specific modality, it's challenging to pinpoint why it's incorrect.

**Option B:** This option is incorrect because it is a common imaging modality that offers relatively high resolution, often comparable to CT scans. However, the exact ranking of imaging modalities can depend on the specific context and the body region being imaged.

**Option C:** This option is incorrect because it represents an imaging modality that offers high resolution, particularly in certain contexts such as musculoskeletal imaging.

**Clinical Pearl / High-Yield Fact**
When choosing an imaging modality, it's essential to consider the specific clinical question being addressed. For instance, a patient with suspected lung cancer may require a high-resolution CT scan, while a patient with a suspected musculoskeletal injury may benefit from an MRI.

**Correct Answer:**
**Correct Answer:** D. Ultrasound.