Correct answer: लगभग 2600–1900 ईसा-पूर्व. The Mature Harappan phase is generally dated to about 2600–1900 BCE. Earlier regional and Early Harappan developments preceded it, and a Late Harappan phase followed after urban decline. Therefore the other options either belong to another chronological phase, a different site, or an older interpretation that does not best fit the evidence. 2600–1900 BCE fits that evidence because it matches the specific chronology, agency and function contained in the question. 600–300 BCE and c. 3200–2800 BCE are genuine historical terms or names, but each belongs to a different office, patron, text, region or sequence. 2600–1900 BCE together with the factual context above, not the isolated option letter.