TASK DEFINITION: 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.
PROBLEM: Passage: In March 1968, CBS and Sony formed CBS/Sony Records, a Japanese business joint venture. With Sony being one of the developers behind the compact disc digital music media, a compact disc production plant was constructed in Japan under the joint venture, allowing CBS to begin supplying some of the first compact disc releases for the American market in 1983.

SOLUTION: In March 1988, CBS and Sony formed what group?

PROBLEM: 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.

SOLUTION: In the US, electric traction became more energy-efficient than what?

PROBLEM: Passage: For much of Eton's history, junior boys had to act as "fags", or servants, to older boys. Their duties included cleaning, cooking, and running errands. A Library member was entitled to yell at any time and without notice, "Boy, Up!" or "Boy, Queue!", and all first-year boys had to come running. The last boy to arrive was given the task. These practices, known as fagging, were partially phased out of most houses in the 1970s. Captains of House and Games still sometimes give tasks to first-year boys, such as collecting the mail from School Office.[citation needed]

SOLUTION:
When was fagging mostly eliminated from all Houses?