D. Wrap an insulated wire around a metal with ferromagnetic properties and apply an electric current.
<u>The magnetic field is turned off when an induced current is not present. </u>
<u>Thus, an electromagnet would act as a magnet </u><em><u>only </u></em><u>when a current is induced in an insulated wire that is wrapped around a material of ferromagnetic material such as iron core rotating in a magnetic field. </u>
It takes a noun and a verb to make a complete sentence. There isn't a single verb in a), b), or c). "Affords" is the verb (predicate) in d)., the only complete sentence.
