Of all the carcinogenic molecules, which one has the most double bonds?
label = '+' mean molecules are carcinogenic; double bond refers to bond_type = ' = ';
SELECT T.molecule_id FROM ( SELECT T3.molecule_id, COUNT(T1.bond_type) FROM bond AS T1 INNER JOIN molecule AS T3 ON T1.molecule_id = T3.molecule_id WHERE T3.label = '+' AND T1.bond_type = '=' GROUP BY T3.molecule_id ORDER BY COUNT(T1.bond_type) DESC LIMIT 1 ) AS T