Atable has several directional compasses, several lengths of wire, a battery, an ammeter, a light bulb, a battery holder and a rubber eraser.
a student is asked to create an electric motor. looking at the materials provided, what other materials would they need?
a) an armature
b) an iron nail.
c) a permanent magnet
d) an electric generator.

I would say answer "a" BUT an armature is the rotating coil or coils of a dynamo or electric motor and if the student already has coils, that wouldn't be the answer. So A is eliminated. 

Now answer "b" sounds right because the student could then create their own armature with a nail and wire... So B is a possible answer choice.

answer "c" is a possibility because an armature is useless without a magnet... so C is a possible choice

and finally "d" if you have batteries, why do you need a generator? what purpose does it serve? D is eliminated.

so the answer is C 

The next element is345640