Input: Read this: There are a number of aids available to pilots, though not all airports are equipped with them. A visual approach slope indicator (VASI) helps pilots fly the approach for landing. Some airports are equipped with a VHF omnidirectional range (VOR) to help pilots find the direction to the airport. VORs are often accompanied by a distance measuring equipment (DME) to determine the distance to the VOR. VORs are also located off airports, where they serve to provide airways for aircraft to navigate upon. In poor weather, pilots will use an instrument landing system (ILS) to find the runway and fly the correct approach, even if they cannot see the ground. The number of instrument approaches based on the use of the Global Positioning System (GPS) is rapidly increasing and may eventually be the primary means for instrument landings.
Question: What also goes along with the VASI?

Output: unanswerable


Input: Read this: Three-phase AC railway electrification was used in Italy, Switzerland and the United States in the early twentieth century. Italy was the major user, for lines in the mountainous regions of northern Italy from 1901 until 1976. The first lines were the Burgdorf-Thun line in Switzerland (1899), and the lines of the Ferrovia Alta Valtellina from Colico to Chiavenna and Tirano in Italy, which were electrified in 1901 and 1902. Other lines where the three-phase system were used were the Simplon Tunnel in Switzerland from 1906 to 1930, and the Cascade Tunnel of the Great Northern Railway in the United States from 1909 to 1927.
Question: How long did three-phase system operate in Cascade Tunnel?

Output: 1909 to 1927


Input: Read this: The apartheid bureaucracy devised complex (and often arbitrary) criteria in the Population Registration Act of 1945 to determine who belonged in which group. Minor officials administered tests to enforce the classifications. When it was unclear from a person's physical appearance whether the individual should be considered Coloured or Black, the "pencil test" was used. A pencil was inserted into a person's hair to determine if the hair was kinky enough to hold the pencil, rather than having it pass through, as it would with smoother hair. If so, the person was classified as Black. Such classifications sometimes divided families.
Question: What test was used to determine if someone was coloured or black?

Output: pencil test


Input: Read this: Network hardware, software and specifications, as well as the expertise of network management personnel are important in ensuring that data follows the most efficient route, and upstream connections work reliably. A tradeoff between cost and efficiency is possible.[citation needed]
Question: Is a tradeoff between efficiency and cost possible? 

Output:
A tradeoff between cost and efficiency is possible