Input: Read this: The key advantage of the four-rail system is that neither running rail carries any current. This scheme was introduced because of the problems of return currents, intended to be carried by the earthed (grounded) running rail, flowing through the iron tunnel linings instead. This can cause electrolytic damage and even arcing if the tunnel segments are not electrically bonded together. The problem was exacerbated because the return current also had a tendency to flow through nearby iron pipes forming the water and gas mains. Some of these, particularly Victorian mains that predated London's underground railways, were not constructed to carry currents and had no adequate electrical bonding between pipe segments. The four-rail system solves the problem. Although the supply has an artificially created earth point, this connection is derived by using resistors which ensures that stray earth currents are kept to manageable levels. Power-only rails can be mounted on strongly insulating ceramic chairs to minimise current leak, but this is not possible for running rails which have to be seated on stronger metal chairs to carry the weight of trains. However, elastomeric rubber pads placed between the rails and chairs can now solve part of the problem by insulating the running rails from the current return should there be a leakage through the running rails.
Question: What does not have to be seated on stronger metal chairs?

Output: unanswerable

Input: Read this: Other notable new vaccines of the period include those for measles (1962, John Franklin Enders of Children's Medical Center Boston, later refined by Maurice Hilleman at Merck), Rubella (1969, Hilleman, Merck) and mumps (1967, Hilleman, Merck) The United States incidences of rubella, congenital rubella syndrome, measles, and mumps all fell by >95% in the immediate aftermath of widespread vaccination. The first 20 years of licensed measles vaccination in the U.S. prevented an estimated 52 million cases of the disease, 17,400 cases of mental retardation, and 5,200 deaths.
Question: When did measles come out?

Output: unanswerable

Input: Read this: The practice has received both advocacy and criticism. Putting clocks forward benefits retailing, sports, and other activities that exploit sunlight after working hours, but can cause problems for evening entertainment and for other activities tied to sunlight, such as farming. Although some early proponents of DST aimed to reduce evening use of incandescent lighting, which used to be a primary use of electricity, modern heating and cooling usage patterns differ greatly and research about how DST affects energy use is limited or contradictory.
Question: What used to be the main draw on electricity?

Output: incandescent lighting

Input: Read this: The subsequent 2005 elections were internationally regarded as the most free and fair in Liberian history. Ellen Johnson Sirleaf, a Harvard-trained economist and former Minister of Finance, was elected as the first female president in Africa. Upon her inauguration, Sirleaf requested the extradition of Taylor from Nigeria and transferred him to the SCSL for trial in The Hague. In 2006, the government established a Truth and Reconciliation Commission to address the causes and crimes of the civil war.
Question: Who was transferred from The Hague for trial in the NIgeria?

Output:
unanswerable