user: Question: What were the revising conventions commentary with a denunciation of 21?
Columns: ['ILO code', 'Field', 'conclusion date', 'entry into force', 'closure for signature', 'Parties (April 2011)', 'Denunciations (September 2011)', 'revising convention(s)', 'text and ratifications']
Types: ['text', 'text', 'text', 'text', 'text', 'real', 'real', 'text', 'text']
Sample row: ['C5', 'Industry', '28 November 1919', '13 June 1921', 'N.A.', 2.0, 70.0, 'C59, this convention', 'Text, ratifications']
SQL:

assistant: SELECT "revising convention(s)" FROM "Table" WHERE "Denunciations (September 2011)" = 21.0;