Question: Extract the answer to the question from the following context. Question: What is the main point of the passage? Context: The development of quadraphonic records was announced in 1971. These recorded four separate sound signals. This was achieved on the two stereo channels by electronic matrixing, where the additional channels were combined into the main signal. When the records were played, phase-detection circuits in the amplifiers were able to decode the signals into four separate channels. There were two main systems of matrixed quadraphonic records produced, confusingly named SQ (by CBS) and QS (by Sansui). They proved commercially unsuccessful, but were an important precursor to later surround-sound systems, as seen in SACD and home cinema today.
Answer: proved commercially unsuccessful, but were an important precursor to later surround-sound systems

Question: Extract the answer to the question from the following context. Question: Where was the largest elemental copper found? Context: Copper is synthesized in massive stars and is present in the Earth's crust at a concentration of about 50 parts per million (ppm), where it occurs as native copper or in minerals such as the copper sulfides chalcopyrite and chalcocite, the copper carbonates azurite and malachite, and the copper(I) oxide mineral cuprite. The largest mass of elemental copper discovered weighed 420 tonnes and was found in 1857 on the Keweenaw Peninsula in Michigan, US. Native copper is a polycrystal, with the largest described single crystal measuring 4.4×3.2×3.2 cm.
Answer: Keweenaw Peninsula in Michigan

Question: Extract the answer to the question from the following context. Question: What was the distance of the furthest location that felt the earthquake? Context: It is also known as the Wenchuan earthquake (Chinese: 汶川大地震; pinyin: Wènchuān dà dìzhèn; literally: "Great Wenchuan earthquake"), after the location of the earthquake's epicenter, Wenchuan County, Sichuan. The epicenter was 80 kilometres (50 mi) west-northwest of Chengdu, the provincial capital, with a focal depth of 19 km (12 mi). The earthquake was also felt in nearby countries and as far away as both Beijing and Shanghai—1,500 km (930 mi) and 1,700 km (1,060 mi) away—where office buildings swayed with the tremor. Strong aftershocks, some exceeding magnitude 6, continued to hit the area even months after the main quake, causing new casualties and damage.
Answer:
1,700 km (1,060 mi)