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: In the former Soviet Union, electric traction eventually became somewhat more energy-efficient than diesel. Partly due to inefficient generation of electricity in the USSR (only 20.8% thermal efficiency in 1950 vs. 36.2% in 1975), in 1950 diesel traction was about twice as energy efficient as electric traction (in terms of net tonne-km of freight per kg of fuel). But as efficiency of electricity generation (and thus of electric traction) improved, by about 1965 electric railways became more efficient than diesel. After the mid 1970s electrics used about 25% less fuel per ton-km. However diesels were mainly used on single track lines with a fair amount of traffic  so that the lower fuel consumption of electrics may be in part due to better operating conditions on electrified lines (such as double tracking) rather than inherent energy efficiency. Nevertheless, the cost of diesel fuel was about 1.5 times more (per unit of heat energy content) than that of the fuel used in electric power plants (that generated electricity), thus making electric railways even more energy-cost effective.
answer:
In the US, electric traction became more energy-efficient than what?


question:
Passage: For temperature studies, subjects must remain awake but calm and semi-reclined in near darkness while their rectal temperatures are taken continuously. Though variation is great among normal chronotypes, the average human adult's temperature reaches its minimum at about 05:00 (5 a.m.), about two hours before habitual wake time. Baehr et al. found that, in young adults, the daily body temperature minimum occurred at about 04:00 (4 a.m.) for morning types but at about 06:00 (6 a.m.) for evening types. This minimum occurred at approximately the middle of the eight hour sleep period for morning types, but closer to waking in evening types.
answer:
What physical factor must be periodicly monitored in temperature studies?


question:
Passage: In addition to the cathedral, Strasbourg houses several other medieval churches that have survived the many wars and destructions that have plagued the city: the Romanesque Église Saint-Étienne, partly destroyed in 1944 by Allied bombing raids, the part Romanesque, part Gothic, very large Église Saint-Thomas with its Silbermann organ on which Wolfgang Amadeus Mozart and Albert Schweitzer played, the Gothic Église protestante Saint-Pierre-le-Jeune with its crypt dating back to the seventh century and its cloister partly from the eleventh century, the Gothic Église Saint-Guillaume with its fine early-Renaissance stained glass and furniture, the Gothic Église Saint-Jean, the part Gothic, part Art Nouveau Église Sainte-Madeleine, etc. The Neo-Gothic church Saint-Pierre-le-Vieux Catholique (there is also an adjacent church Saint-Pierre-le-Vieux Protestant) serves as a shrine for several 15th-century wood worked and painted altars coming from other, now destroyed churches and installed there for public display. Among the numerous secular medieval buildings, the monumental Ancienne Douane (old custom-house) stands out.
answer:

In what century was the Eglise Saint-Etienne constructed?