Final answer:
X-ray diffraction is used to study the structures of proteins, crystals, and other crystalline substances, hence the correct answer is D) All of the Above.
Step-by-step explanation:
X-ray diffraction is a technique used extensively to study the structure of various materials. Specifically, it is utilized to probe the atomic and molecular structure within crystals, as well as complex arrangements in materials such as proteins and high-temperature superconductors. X-ray crystallography, a method that employs x-ray diffraction, has been instrumental in the discovery of DNA’s double-helix structure and in current research where the lattice arrangements are crucial for the properties of the material, like superconductivity.
So, in answer to the student's question regarding what structures X-ray diffraction is used to study, the answer would be D) All of the Above, as it is used to study the structure of proteins, crystals, and other crystalline materials.