Which paper ID cited the most word? In which class label does it belongs to?
most cited word refers to max(word_cited_id);
SELECT T1.paper_id, T1.class_label FROM paper AS T1 INNER JOIN content AS T2 ON T1.paper_id = T2.paper_id GROUP BY T1.paper_id, T1.class_label ORDER BY COUNT(T2.word_cited_id) DESC LIMIT 1