An Electron Microscope Must Use Electromagnet 'Lenses'shaped Like Donuts to Direct

Multiple Choice

An electron microscope must use electromagnet 'lenses'shaped like donuts to direct the electrons onto the specimen.Why aren't they solid,like the lenses in a light microscope?

A) A magnetic field cannot be applied across a completely solid object-there must be an opening within the object for the field to be applied through.
B) The user has to be able to physically look through the magnets to focus the beam of electrons onto the specimen,since the metal of the magnets is opaque.Without a hole in the middle,the user wouldn't be able to see!
C) The electrons would destroy the electromagnet material unless there was a physical hole for them to travel through on their way to the specimen.
D) Electrons are particles,and particles cannot travel through a solid item.The hole in the middle allows them to travel from the source of the electrons to the specimen.