Task: Question Answering
Input (English): Passage: In Iran (Persia), the history of cotton dates back to the Achaemenid era (5th century BC); however, there are few sources about the planting of cotton in pre-Islamic Iran. The planting of cotton was common in Merv, Ray and Pars of Iran. In Persian poets' poems, especially Ferdowsi's Shahname, there are references to cotton ("panbe" in Persian). Marco Polo (13th century) refers to the major products of Persia, including cotton. John Chardin, a French traveler of the 17th century who visited the Safavid Persia, spoke approvingly of the vast cotton farms of Persia. Question: Use of cotton in Iran dates back to what period?
Output (English): Achaemenid era