Correct answer: Pyran (2H-pyran)
Isoxazole and 1,3-thiazole are aromatic five-membered heterocycles: a lone pair from O or S (and the ring double bonds) supplies six pi electrons in a planar conjugated ring. The pyrylium ion is an aromatic six-membered oxygen cation (6 pi electrons, like a charged benzene). 2H-Pyran, however, contains an sp3 -CH2- carbon that breaks the cyclic conjugation, so it cannot be aromatic and is non-aromatic.