Database: toxicology
Question: What is the molecule of atom id "TR000_2" and atom id 2 "TR000_4"?
SQL: SELECT T1.molecule_id FROM bond AS T1 INNER JOIN connected AS T2 ON T1.bond_id = T2.bond_id WHERE T2.atom_id = 'TR000_2' AND T2.atom_id2 = 'TR000_4'