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.
--------
Question: Tennessee furnished more soldiers for the Confederate Army than any other state, and more soldiers for the Union Army than any other Southern state. Beginning during Reconstruction, it had competitive party politics, but a Democratic takeover in the late 1880s resulted in passage of disfranchisement laws that excluded most blacks and many poor whites from voting. This sharply reduced competition in politics in the state until after passage of civil rights legislation in the mid-20th century. In the 20th century, Tennessee transitioned from an agrarian economy to a more diversified economy, aided by massive federal investment in the Tennessee Valley Authority and, in the early 1940s, the city of Oak Ridge. This city was established to house the Manhattan Project's uranium enrichment facilities, helping to build the world's first atomic bomb, which was used during World War II.

Answer: Which part dominated Tennessee's politics in the late 1880s?

Question: After 1870, the new railroads across the Plains brought hunters who killed off almost all the bison for their hides. The railroads offered attractive packages of land and transportation to European farmers, who rushed to settle the land. They (and Americans as well) also took advantage of the homestead laws to obtain free farms. Land speculators and local boosters identified many potential towns, and those reached by the railroad had a chance, while the others became ghost towns. In Kansas, for example, nearly 5000 towns were mapped out, but by 1970 only 617 were actually operating. In the mid-20th century, closeness to an interstate exchange determined whether a town would flourish or struggle for business.

Answer: after about what year did railroads bring hunters to the great plains?

Question: 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:
What type of trains became more energy-efficient in the former Soviet Union?