Why Did Early Agricultural Settlements Arise in the Indus Valley

Why did early agricultural settlements arise in the Indus Valley before the Ganges Valley?

A) Annual floods replenished the soil in the Indus Valley but not in the Ganges Valley.
B) The Indus River,but not the Ganges River,brought plentiful water from its source in the Himalayas.
C) The Indus Valley suffered less from the yearly monsoons than did the Ganges Valley.
D) The Ganges Valley,unlike the Indus Valley,was surrounded by inhospitable deserts.