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:
The Mongols learned from captives of the abundant green pastures beyond the Bulgar territory, allowing for the planning for conquest of Hungary and Europe. Genghis Khan recalled Subutai back to Mongolia soon afterwards, and Jebe died on the road back to Samarkand. The famous cavalry expedition led by Subutai and Jebe, in which they encircled the entire Caspian Sea defeating all armies in their path, remains unparalleled to this day, and word of the Mongol triumphs began to trickle to other nations, particularly Europe. These two campaigns are generally regarded as reconnaissance campaigns that tried to get the feel of the political and cultural elements of the regions. In 1225 both divisions returned to Mongolia. These invasions added Transoxiana and Persia to an already formidable empire while destroying any resistance along the way. Later under Genghis Khan's grandson Batu and the Golden Horde, the Mongols returned to conquer Volga Bulgaria and Kievan Rus' in 1237, concluding the campaign in 1240.
Answer:
Which Mongol leader completed the conquest of Kievan Rus'?