Which of the following statements is not true about the Indus Valley civilization? A. Many cities grew up in the valley of the Indus River, including Harappa and Mohenjo-Daro. B. The people of the Indus Valley invented a complex system of writing. C. The Indus Valley farmers grew a surplus of wheat, barley, and a variety of fruits. D. Almost all the people of the Indus Valley were farmers.