Explanation:

According to Indian Census data, Kanpur became a million-plus city in 1961, and Lucknow became a million-plus city in 1981. Given the options, option (c) '1971 and 1981 respectively' correctly identifies Lucknow's year, though Kanpur's year is listed as 1971 instead of 1961. This option is the closest fit among the choices, assuming a slight discrepancy for Kanpur's first million-city status in the question's context.