The correct option is A 2500 BC
The Aryans were a semi-nomadic pastoral people. By 1500 BCE the Aryans migrated into the Indian subcontinent. Coming from central Asia, this large group of nomadic cattle herders crossed the Hindu Kush Mountains and came in contact with the Indus Valley Civilization. Hence, Option A is correct. The 6500 BC was of the Neolithic age, 3500 BC saw the first civilisation in Mesopotamia, 8000 BC was the Mesolithic Period. The Proto-Indo-Iranians, from which the Indo-Aryans developed, are identified with the Sintashta culture (2100–1800 BCE), and the Andronovo culture, which flourished. 1800–1400 BCE in the steppes around the Aral sea, present-day Kazakhstan, Uzbekistan, and Turkmenistan. Since none of these timelines corresponds to the Aryan migration, these are incorrect.