Why does the professor mention that the Moon lacks a magnetic field? A. To point out the danger inherent in mining for helium-3 on the Moon B. To point out a flaw in the theory that helium-3 can be found on the Moon's surface C. To explain why it was difficult for astronauts to detect helium-3 on the Moon D. To explain why it is likely that there are large amounts of helium-3 on the Moon