What was the cause of conflict between iraq and iran in 1980

Iraq invaded Iran on 22 September 1980, triggering a bitter eight-year war which destabilized the region and devastated both countries. The then Iraqi leader Saddam Hussein claimed as a reason for the invasion a territorial dispute over the Shatt al-Arab, the waterway which forms the boundary between the two countries.

answer; ///i do believe that the correct answer is (b) ///middle colony