According to Modern Dynamo Theory, the Production of a Planetwide

Multiple Choice

According to modern dynamo theory, the production of a planetwide magnetic field around a terrestrial-type planet appears to require

A) rapid rotation and a molten metallic core.
B) a permanently magnetized solid metallic core.
C) a molten metallic core, with or without rotation.
D) rapid rotation and a metallic core, either solid or molten.