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: There has, however, been interest among railroad operators in returning to DC use at higher voltages than previously used. At the same voltage, DC often has less loss than AC, and for this reason high-voltage direct current is already used on some bulk power transmission lines. DC avoids the electromagnetic radiation inherent with AC, and on a railway this also reduces interference with signalling and communications and mitigates hypothetical EMF risks. DC also avoids the power factor problems of AC. Of particular interest to railroading is that DC can supply constant power with a single ungrounded wire. Constant power with AC requires three-phase transmission with at least two ungrounded wires. Another important consideration is that mains-frequency 3-phase AC must be carefully planned to avoid unbalanced phase loads. Parts of the system are supplied from different phases on the assumption that the total loads of the 3 phases will even out. At the phase break points between regions supplied from different phases, long insulated supply breaks are required to avoid them being shorted by rolling stock using more than one pantograph at a time. A few railroads have tried 3-phase but its substantial complexity has made single-phase standard practice despite the interruption in power flow that occurs twice every cycle. An experimental 6 kV DC railway was built in the Soviet Union.

SOLUTION: Railroad operators have shown little interest in returning to what?

PROBLEM: Passage: A fine tribute to the fall of Warsaw and history of Poland can be found in the Warsaw Uprising Museum and in the Katyń Museum which preserves the memory of the crime. The Warsaw Uprising Museum also operates a rare preserved and operating historic stereoscopic theatre, the Warsaw Fotoplastikon. The Museum of Independence preserves patriotic and political objects connected with Poland's struggles for independence. Dating back to 1936 Warsaw Historical Museum contains 60 rooms which host a permanent exhibition of the history of Warsaw from its origins until today.

SOLUTION: Where can a tribute to the fall of Katyn be found?

PROBLEM: Passage: Until 1917, it was possible for someone who was not a priest, but only in minor orders, to become a cardinal (see "lay cardinals", below), but they were enrolled only in the order of cardinal deacons. For example, in the 16th century, Reginald Pole was a cardinal for 18 years before he was ordained a priest. In 1917 it was established that all cardinals, even cardinal deacons, had to be priests, and, in 1962, Pope John XXIII set the norm that all cardinals be ordained as bishops, even if they are only priests at the time of appointment. As a consequence of these two changes, canon 351 of the 1983 Code of Canon Law requires that a cardinal be at least in the order of priesthood at his appointment, and that those who are not already bishops must receive episcopal consecration. Several cardinals aged over 80 or close to it when appointed have obtained dispensation from the rule of having to be a bishop. These were all appointed cardinal-deacons, but one of them, Roberto Tucci, lived long enough to exercise the right of option and be promoted to the rank of cardinal-priest.

SOLUTION:
What was possible for someone to become who was not a priest, but only in major orders?