Database: toxicology
Question: What is the type of the bond which is presenting the connection between two atoms TR000_1 and TR000_2?
SQL: SELECT T1.bond_type FROM bond AS T1 INNER JOIN connected AS T2 ON T1.bond_id = T2.bond_id WHERE T2.atom_id = 'TR000_1' AND T2.atom_id2 = 'TR000_2'