This task is about reading the given passage and construct a question about the information present in the passage. Construct a question in such a way that (i) it is unambiguous, (ii) it is answerable from the passage, (iii) its answer is unique (iv) its answer is a continuous text span from the paragraph. Avoid creating questions that (i) can be answered correctly without actually understanding the paragraph and (ii) uses same words or phrases given in the passage.

Let me give you an example: Passage: The French and Indian War (1754–1763) was the North American theater of the worldwide Seven Years' War. The war was fought between the colonies of British America and New France, with both sides supported by military units from their parent countries of Great Britain and France, as well as Native American allies. At the start of the war, the French North American colonies had a population of roughly 60,000 European settlers, compared with 2 million in the British North American colonies. The outnumbered French particularly depended on the Indians. Long in conflict, the metropole nations declared war on each other in 1756, escalating the war from a regional affair into an intercontinental conflict.
The answer to this example can be: When was the French and Indian War?
Here is why: This question is based on the following sentence in the passage- The French and Indian War (1754–1763) was the North American theater of the worldwide Seven Years' War. It is a common convention to write (start year-end year) beside a historical event to understand when the event happened. You can ask questions like this one about dates, years, other numerals, persons, locations, noun phrases, verb phrases, adjectives, clauses etc. which exist in the paragraph.

OK. solve this:
These scholars suggest, from their studies of economic and social data, that early 20th-century child labour in Europe and the United States ended in large part as a result of the economic development of the formal regulated economy, technology development and general prosperity. Child labour laws and ILO conventions came later. Edmonds suggests, even in contemporary times, the incidence of child labour in Vietnam has rapidly reduced following economic reforms and GDP growth. These scholars suggest economic engagement, emphasis on opening quality schools rather than more laws and expanding economically relevant skill development opportunities in the third world. International legal actions, such as trade sanctions increase child labour.
Answer:
What caused child labour to decrease in the 20th century?