Why Is It Surprising That Mercury's Magnetic Field Is Strong

Multiple Choice

Why is it surprising that Mercury's magnetic field is strong enough to be measured (> >Earth's moon's) ,yet significantly weaker than Earth's magnetic field?

A) Mercury's density suggests its core is like Earth's,so its magnetic field should be of nearly equal strength.
B) Mercury is hot enough that its core should be very molten and produce a magnetic field larger than Earth's.
C) Mercury's small size suggests that it should no longer have a molten core,so no magnetic field is expected.
D) Mercury rotates so slowly that it should not be able to produce a magnetic field.
E) Mercury is so close to the sun that its magnetic field should be destroyed by the solar wind.