In General, Small Bodies in the Solar System Are Less

In general, small bodies in the solar system are less likely than large bodies to possess a planet-wide magnetic field. Why should we expect size and magnetism to be correlated?

A) A small body cools more rapidly and is less likely to possess a molten, liquid interior-one requirement for planet-wide magnetism.
B) Small bodies are more likely to be heavily cratered, and such impacts can destroy the mechanism that produces the magnetic field.
C) Magnetic fields are produced by the entire volume of a body. Smaller bodies have smaller volumes and hence smaller magnetic fields.
D) Small bodies necessarily rotate more slowly, and a rapid rotation rate is one requirement for a planet-wide magnetic field.