D

Step 1: A vibration magnetometer is an instrument used to measure the strength of magnetic fields. It operates on the principle of vibrations induced by a magnetic field acting on a magnetic dipole.
Step 2: It can be used to compare different magnetic fields. Thus, it can evaluate both the Earth's magnetic field and other magnetic fields.
Step 3: Additionally, the instrument can be employed to compare magnetic moments of different magnets by analyzing their oscillations in a uniform magnetic field.
Step 4: Since the vibration magnetometer serves to compare magnetic fields, Earth's magnetic field, and magnetic moments, the correct answer is that it can be used for all these comparisons.
Therefore, the correct answer is: D.