instruction:
This task is about creating an unanswerable question based on a given passage. Construct a question that looks relevant to the given context but is unanswerable. Following are a few suggestions about how to create unanswerable questions:
(i) create questions which require satisfying a constraint that is not mentioned in the passage
(ii) create questions which require information beyond what is provided in the passage in order to answer
(iii) replace an existing entity, number, date mentioned in the passage with other entity, number, date and use it in the question
(iv) create a question which is answerable from the passage and then replace one or two words by their antonyms or insert/remove negation words to make it unanswerable.
question:
Passage: Bermuda's pink sand beaches and clear, cerulean blue ocean waters are popular with tourists. Many of Bermuda's hotels are located along the south shore of the island. In addition to its beaches, there are a number of sightseeing attractions. Historic St George's is a designated World Heritage Site. Scuba divers can explore numerous wrecks and coral reefs in relatively shallow water (typically 30–40 ft or 9–12 m in depth), with virtually unlimited visibility. Many nearby reefs are readily accessible from shore by snorkellers, especially at Church Bay.
answer:
What are located along the shore of the coral reefs?


question:
Passage: About 75% of the population is employed in subsistence agriculture upon Swazi Nation Land (SNL). In contrast with the commercial farms, Swazi Nation Land suffers from low productivity and investment. This dual nature of the Swazi economy, with high productivity in textile manufacturing and in the industrialised agricultural TDLs on the one hand, and declining productivity subsistence agriculture (on SNL) on the other, may well explain the country's overall low growth, high inequality and unemployment.
answer:
Where does the population get 75% of its income?


question:
Passage: Near the end of the 19th century compound engines came into widespread use. Compound engines exhausted steam in to successively larger cylinders to accommodate the higher volumes at reduced pressures, giving improved efficiency. These stages were called expansions, with double and triple expansion engines being common, especially in shipping where efficiency was important to reduce the weight of coal carried. Steam engines remained the dominant source of power until the early 20th century, when advances in the design of electric motors and internal combustion engines gradually resulted in the replacement of reciprocating (piston) steam engines, with shipping in the 20th-century relying upon the steam turbine.
answer:

What type of engines became widespread around the end of the 20th century?