The correct option is B It is a magnet which collects all the magnetic material inside the cow.
Cow magnets are popular with dairy farmers and veterinarians to help cure or prevent Hardware disease in cattle. While grazing, cows eat everything from grass and dirt to nails, staples, and bits of metal wires. Therefore, a cow magnet is used to collect all the magnetic materials inside a cow and safely disposes them out through the dung.