Question: What are the response received dates for the documents described as 'Regular'?
SQL: SELECT T1.response_received_date FROM Documents AS T1 JOIN Document_Types AS T2 ON T1.document_type_code   =   T2.document_type_code JOIN Grants AS T3 ON T1.grant_id   =   T3.grant_id WHERE T2.document_description   =   'Regular'