The correct chronological order of the Secretary Generals of the United Nations is U. Thant, K. Waldheim, B.B. Ghali, and K. Annan.
Option 1 is the correct answer as it correctly lists the Secretary Generals in the order: U. Thant, K. Waldheim, B.B. Ghali, and K. Annan.
Option 2 is incorrect as it reverses the order of U. Thant and K. Waldheim.
Option 3 is incorrect as it has K. Annan listed before B.B. Ghali, which is not the correct chronological order.
Option 4 is also incorrect as it has K. Annan listed last, after K. Waldheim, which is not the correct order.
In conclusion, the correct chronological order of the Secretary Generals of the United Nations is U. Thant, K. Waldheim, B.B. Ghali, and K. Annan, as stated in option 1.