Input: Read this: A railway electrification system supplies electric power to railway trains and trams without an on-board prime mover or local fuel supply. Electrification has many advantages but requires significant capital expenditure. Selection of an electrification system is based on economics of energy supply, maintenance, and capital cost compared to the revenue obtained for freight and passenger traffic. Different systems are used for urban and intercity areas; some electric locomotives can switch to different supply voltages to allow flexibility in operation.
Question: What are two types of revenue obtained through railway transportation?

Output: freight and passenger traffic

Input: Read this: The first historical mention of the use of hops in beer was from 822 AD in monastery rules written by Adalhard the Elder, also known as Adalard of Corbie, though the date normally given for widespread cultivation of hops for use in beer is the thirteenth century. Before the thirteenth century, and until the sixteenth century, during which hops took over as the dominant flavouring, beer was flavoured with other plants; for instance, grains of paradise or alehoof. Combinations of various aromatic herbs, berries, and even ingredients like wormwood would be combined into a mixture known as gruit and used as hops are now used. Some beers today, such as Fraoch' by the Scottish Heather Ales company and Cervoise Lancelot by the French Brasserie-Lancelot company, use plants other than hops for flavouring.
Question: What name was Adalhard the Elder also known as in 822 AD?

Output: Adalard of Corbie

Input: Read this: In some languages, such as English, aspiration is allophonic. Stops are distinguished primarily by voicing, and voiceless stops are sometimes aspirated, while voiced stops are usually unaspirated.
Question: Voiceless stops are at times what?

Output: aspirated

Input: Read this: This first list is referred to as the "Class of '67" in The Endangered Species Act at Thirty, Volume 1, which concludes that habitat destruction, the biggest threat to those 78 species, is still the same threat to the currently listed species. It included only vertebrates because the Department of Interior's definition of "fish and wildlife" was limited to vertebrates. However, with time, researchers noticed that the animals on the endangered species list still were not getting enough protection, thus further threatening their extinction. The endangered species program was expanded by the Endangered Species Act of 1969.
Question: What volume was published in 1969?

Output:
unanswerable