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.

Passage: The army is led by a civilian Secretary of the Army, who has the statutory authority to conduct all the affairs of the army under the authority, direction and control of the Secretary of Defense. The Chief of Staff of the Army, who is the highest-ranked military officer in the army, serves as the principal military adviser and executive agent for the Secretary of the Army, i.e., its service chief; and as a member of the Joint Chiefs of Staff, a body composed of the service chiefs from each of the four military services belonging to the Department of Defense who advise the President of the United States, the Secretary of Defense, and the National Security Council on operational military matters, under the guidance of the Chairman and Vice Chairman of the Joint Chiefs of Staff. In 1986, the Goldwater–Nichols Act mandated that operational control of the services follows a chain of command from the President to the Secretary of Defense directly to the unified combatant commanders, who have control of all armed forces units in their geographic or function area of responsibility. Thus, the secretaries of the military departments (and their respective service chiefs underneath them) only have the responsibility to organize, train and equip their service components. The army provides trained forces to the combatant commanders for use as directed by the Secretary of Defense. Question: Who does the Chief of Staff serve as the principal military adviser to?
Secretary of the Army

Passage: In 1853 the Russian Empire on behalf of the Slavic Balkan states began to question the very existence of the Ottoman Empire. The result was the Crimean War, 1853–1856, in which the British Empire and the French Empire supported the Ottoman Empire in its struggle against the incursions of the Russian Empire. Eventually, the Ottoman Empire lost control of the Balkan region. Question: What was the Ottoman Empire's struggle against in the Crimean War?
the incursions of the Russian Empire

Passage: City and Guilds College was founded in 1876 from a meeting of 16 of the City of London's livery companies for the Advancement of Technical Education (CGLI), which aimed to improve the training of craftsmen, technicians, technologists, and engineers. The two main objectives were to create a Central Institution in London and to conduct a system of qualifying examinations in technical subjects. Faced with their continuing inability to find a substantial site, the Companies were eventually persuaded by the Secretary of the Science and Art Department, General Sir John Donnelly (who was also a Royal Engineer) to found their institution on the eighty-seven acre (350,000 m²) site at South Kensington bought by the 1851 Exhibition Commissioners (for GBP 342,500) for 'purposes of art and science' in perpetuity. The latter two colleges were incorporated by Royal Charter into the Imperial College of Science and Technology and the CGLI Central Technical College was renamed the City and Guilds College in 1907, but not incorporated into Imperial College until 1910. Question: What was the aim of the City and Guilds College when it was founded?

improve the training of craftsmen, technicians, technologists, and engineers