This task is about writing a correct answer for the reading comprehension task. Based on the information provided in a given passage, you should identify the shortest continuous text span from the passage that serves as an answer to the given question. Avoid answers that are incorrect or provides incomplete justification for the question.

Input: Consider Input: Passage: In the following year, Bell became professor of Vocal Physiology and Elocution at the Boston University School of Oratory. During this period, he alternated between Boston and Brantford, spending summers in his Canadian home. At Boston University, Bell was "swept up" by the excitement engendered by the many scientists and inventors residing in the city. He continued his research in sound and endeavored to find a way to transmit musical notes and articulate speech, but although absorbed by his experiments, he found it difficult to devote enough time to experimentation. While days and evenings were occupied by his teaching and private classes, Bell began to stay awake late into the night, running experiment after experiment in rented facilities at his boarding house. Keeping "night owl" hours, he worried that his work would be discovered and took great pains to lock up his notebooks and laboratory equipment. Bell had a specially made table where he could place his notes and equipment inside a locking cover. Worse still, his health deteriorated as he suffered severe headaches. Returning to Boston in fall 1873, Bell made a fateful decision to concentrate on his experiments in sound. Question: In what year did Bell start to focus on research into sound?

Output: 1873


Input: Consider Input: Passage: The Bell Telephone Company was created in 1877, and by 1886, more than 150,000 people in the U.S. owned telephones. Bell Company engineers made numerous other improvements to the telephone, which emerged as one of the most successful products ever. In 1879, the Bell company acquired Edison's patents for the carbon microphone from Western Union. This made the telephone practical for longer distances, and it was no longer necessary to shout to be heard at the receiving telephone. Question: What addition let people stop yelling into the telephone?

Output: carbon microphone


Input: Consider Input: Passage: Beginning in the 1940s and continuing into the 1970s, the bureau investigated cases of espionage against the United States and its allies. Eight Nazi agents who had planned sabotage operations against American targets were arrested, and six were executed (Ex parte Quirin) under their sentences. Also during this time, a joint US/UK code-breaking effort (the Venona project)—with which the FBI was heavily involved—broke Soviet diplomatic and intelligence communications codes, allowing the US and British governments to read Soviet communications. This effort confirmed the existence of Americans working in the United States for Soviet intelligence. Hoover was administering this project but failed to notify the Central Intelligence Agency (CIA) until 1952. Another notable case is the arrest of Soviet spy Rudolf Abel in 1957. The discovery of Soviet spies operating in the US allowed Hoover to pursue his longstanding obsession with the threat he perceived from the American Left, ranging from Communist Party of the United States of America (CPUSA) union organizers to American liberals. Question: When did the FBI begin investigating espionage?


Output: 1940s