International organizations (UN): Choose the set that lists UN Secretaries-General in correct chronological order (earlier → later). Consider the mid-20th century sequence. Select the correctly ordered set.

Given data

• Task: Order UN Secretaries-General chronologically.
• Names involved: Trygve Lie, Dag Hammarskjöld, U Thant, Kurt Waldheim.

Concept/Approach
Recall the early UN leadership timeline: Lie (1946–1952), Hammarskjöld (1953–1961), U Thant (1961–1971), Waldheim (1972–1981).

Step-by-step reasoning
• First: Trygve Lie (post-WWII founding period). • Second: Dag Hammarskjöld. • Third: U Thant. • Fourth: Kurt Waldheim.

Common pitfalls
Swapping U Thant and Hammarskjöld or placing Waldheim too early.

Final Answer
Trygve Lie → Dag Hammarskjöld → U Thant → Kurt Waldheim