What creates Earth's magnetic field?

A) movement of ocean plates B) mantle convection currents C) continental plate movement D) radiation

Earth's magnetic field doesn't have much to do with tectonic plates. But both are caused by movement of the magma. The magnetic field is caused by electrical currents flowing in the magma, roughly parallel with the Equator. Tectonic plates move around the surface of the Earth over the liquid magma.

So I'd go with B. mantle convection currents