Which of the following is not a member of ‘Gulf Cooperation Council’?

Which of the following is not a member of ‘Gulf Cooperation Council’?

Iran
Saudi Arabia
Oman
Kuwait
This question was previously asked in
UPSC IAS – 2016
The Gulf Cooperation Council (GCC) is a regional intergovernmental political and economic union consisting of all Arab states of the Persian Gulf, except Iraq. Its members are Saudi Arabia, Kuwait, the United Arab Emirates, Qatar, Bahrain, and Oman. Among the options provided, Saudi Arabia, Oman, and Kuwait are members of the GCC. Iran is not a member; it is located across the Persian Gulf but is not an Arab state and has historically had complex relations with GCC members.
The Gulf Cooperation Council (GCC) is a political and economic alliance of six Middle Eastern countries: Saudi Arabia, Kuwait, UAE, Qatar, Bahrain, and Oman.
The GCC was established in 1981. Its headquarters are located in Riyadh, Saudi Arabia. The main purpose of the GCC is to enhance cooperation and coordination among its member states in various fields, including politics, economy, defense, security, and social affairs.