Option b is the correct answer. According to the Chachnama, the capital of the Indus Country (Sindh) in the 6th and 7th centuries was "Arod". The Chachnama, also known as the Chach Nama or Fateh nama Sindh, is a historical source that provides insights into the history of Sindh in the 7th and 8th centuries CE. It was written in Classical Persian and is attributed to 'Ali Kufi, although there is debate about its authorship. The Chachnama chronicles the Arab conquest of Sindh and the events leading up to it.