The correct options are
B 'X' was established in 1945.
C All of the world's major countries are a part of 'X'.
D As of 2020, Antonio Guterres is the Secretary General of 'X'.
In the above given question, 'X' refers to the United Nations. It replaced the League of Nations that failed to prevent another world war. It was formed in 1945 after the end of WWII. It was founded by the Charter of the United Nations and Statue of the International Court of Justice. Its main mandate was to establish collective security and maintain world peace. The United Nations also works in protecting human rights, delivering humanitarian aid, promoting sustainable development, and upholding international law.