The problem: Answer a question about this article:
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.
What are two types of revenue obtained through railway transportation?
****
The answer: freight and passenger traffic

The problem: Answer a question about this article:
The book was written for non-specialist readers and attracted widespread interest upon its publication. As Darwin was an eminent scientist, his findings were taken seriously and the evidence he presented generated scientific, philosophical, and religious discussion. The debate over the book contributed to the campaign by T. H. Huxley and his fellow members of the X Club to secularise science by promoting scientific naturalism. Within two decades there was widespread scientific agreement that evolution, with a branching pattern of common descent, had occurred, but scientists were slow to give natural selection the significance that Darwin thought appropriate. During "the eclipse of Darwinism" from the 1880s to the 1930s, various other mechanisms of evolution were given more credit. With the development of the modern evolutionary synthesis in the 1930s and 1940s, Darwin's concept of evolutionary adaptation through natural selection became central to modern evolutionary theory, and it has now become the unifying concept of the life sciences.
What section of the population was Darwin's book written for?
****
The answer: non-specialist readers

The problem: Answer a question about this article:
The superstructure of a carrier (such as the bridge, flight control tower) are concentrated in a relatively small area called an island, a feature pioneered on the HMS Hermes in 1923. While the island is usually built on the starboard side of the fight deck, the Japanese aircraft carriers Akagi and Hiryu had their islands built on the port side. Very few carriers have been designed or built without an island. The flush deck configuration proved to have significant drawbacks, primary of which was management of the exhaust from the power plant. Fumes coming across the deck were a major issue in USS Langley. In addition, lack of an island meant difficulties managing the flight deck, performing air traffic control, a lack of radar housing placements and problems with navigating and controlling the ship itself.
What was the biggest drawback to the flush deck configuration?
****
The answer: management of the exhaust from the power plant

The problem: Answer a question about this article:
From the late 10th to late 7th centuries BC, the Iranian peoples, together with the pre-Iranian kingdoms, fell under the domination of the Assyrian Empire, based in northern Mesopotamia. Under king Cyaxares, the Medes and Persians entered into an alliance with Nabopolassar of Babylon, as well as the Scythians and the Cimmerians, and together they attacked the Assyrian Empire. The civil war ravaged the Assyrian Empire between 616 BC and 605 BC, thus freeing their respective peoples from three centuries of Assyrian rule. The unification of the Median tribes under a single ruler in 728 BC led to the foundation of the Median Empire which, by 612 BC, controlled the whole Iran and the eastern Anatolia. This marked the end of the Kingdom of Urartu as well, which was subsequently conquered and dissolved.
When did the Median tribes unify under a single ruler to form the Median Empire?
****
The answer:
728 BC