One grоup оf students is investigаting the prоperties of the bаr mаgnet shown below. The students took a bowl of iron nails, plastic pieces, wood shavings, and paper pieces. The bar magnet was placed inside the bowl for some time and then taken out. Several iron nails were stuck on the bar magnet. The experiment was repeated by several students using different bar magnets. Based on the investigations, which of these theories would the students most likely propose? (2 points)