Problem: Question: "What issue led to the horns getting wraped with tape?"  Context: "Delicate sounds and fine overtones were mostly lost, because it took a lot of sound energy to vibrate the recording horn diaphragm and cutting mechanism. There were acoustic limitations due to mechanical resonances in both the recording and playback system. Some pictures of acoustic recording sessions show horns wrapped with tape to help mute these resonances. Even an acoustic recording played back electrically on modern equipment sounds like it was recorded through a horn, notwithstanding a reduction in distortion because of the modern playback. Toward the end of the acoustic era, there were many fine examples of recordings made with horns."  Answer:

A: mechanical resonances


Problem: Question: "At what point was the key river on the continent controlled?"  Context: "The Byzantine Empire ruled the northern shores of the Sahara from the 5th to the 7th centuries. After the Muslim conquest of Arabia (Arabian peninsula) the Muslim conquest of North Africa began in the mid-7th to early 8th centuries, Islamic influence expanded rapidly on the Sahara. By the end of 641 all of Egypt was in Muslim hands. The trade across the desert intensified. A significant slave trade crossed the desert. It has been estimated that from the 10th to 19th centuries some 6,000 to 7,000 slaves were transported north each year."  Answer:

A: By the end of 641


Problem: Question: "Were more incendiaries dropped on the 9th or the 25th?"  Context: "In the north, substantial efforts were made against Newcastle-upon-Tyne and Sunderland, which were large ports on the English east coast. On 9 April 1941 Luftflotte 2 dropped 150 tons of high explosives and 50,000 incendiaries from 120 bombers in a five-hour attack. Sewer, rail, docklands, and electric installations were damaged. In Sunderland on 25 April, Luftflotte 2 sent 60 bombers which dropped 80 tons of high explosive and 9,000 incendiaries. Much damage was done. A further attack on the Clyde, this time at Greenock, took place on 6 and 7 May. However, as with the attacks in the south, the Germans failed to prevent maritime movements or cripple industry in the regions."  Answer:

A: 9 April


Problem: Question: "What people were on the ground fighting during the takeover?"  Context: "The Russian Revolution is the series of revolutions in Russia in 1917, which destroyed the Tsarist autocracy and led to the creation of the Soviet Union. Following the abdication of Nicholas II of Russia, the Russian Provisional Government was established. In October 1917, a red faction revolution occurred in which the Red Guard, armed groups of workers and deserting soldiers directed by the Bolshevik Party, seized control of Saint Petersburg (then known as Petrograd) and began an immediate armed takeover of cities and villages throughout the former Russian Empire."  Answer:

A:
armed groups of workers and deserting soldiers