## Core Concept
The question tests understanding of techniques used in molecular biology and biophysics to study the structure of molecules. **X-ray crystallography**, **Nuclear Magnetic Resonance (NMR) spectroscopy**, and **Cryoelectron microscopy** are key methods used for determining the three-dimensional structures of molecules, such as proteins and nucleic acids.

## Why the Correct Answer is Right
The correct answer, **X-ray crystallography**, is a technique used to determine the three-dimensional structure of molecules, including proteins and nucleic acids. It involves crystallizing the molecule of interest and then using X-rays to produce a diffraction pattern, which can be used to determine the detailed structure of the molecule. This method has been instrumental in understanding the structure-function relationships of biological macromolecules.

## Why Each Wrong Option is Incorrect
* **Option A:** While there are various techniques used in molecular biology, without the specific details of option A, it's challenging to directly refute it. However, assuming it's not X-ray crystallography, NMR spectroscopy, or Cryoelectron microscopy, it likely doesn't directly pertain to structure determination at the molecular level.
* **Option B:** Similarly, without specifics, it's hard to directly address option B. If it's not one of the primary structure determination techniques, it might relate to other aspects of molecular analysis, such as sequencing or functional studies.
* **Option D:** This option is also unspecified but presumably does not represent a primary method for studying the structure of molecules.

## Clinical Pearl / High-Yield Fact
A key point to remember is that **X-ray crystallography** and **NMR spectroscopy** are foundational techniques in structural biology. Understanding the strengths and limitations of each is crucial. For example, X-ray crystallography requires a crystalline sample and can provide high-resolution structures, while NMR spectroscopy can provide structural information in solution but often at lower resolution.

## Correct Answer Line
**Correct Answer: C. X-ray crystallography**