If a secondary coil is present, the dying magnetic field of the primary creates a strong current in the secondary which makes the lower horseshoe into an electromagnet.
(a secondary coil; is; present) (the dying magnetic field of the primary; creates; a strong current in the secondary which makes the lower horseshoe into an electromagnet) (a strong current in the secondary; makes; the lower horseshoe)
a secondary coil the dying magnetic field of the primary a strong current in the secondary
is creates makes
present
a strong current in the secondary which makes the lower horseshoe into an electromagnet
the lower horseshoe