Input: Article: Before Prince Albert's death, the palace was frequently the scene of musical entertainments, and the greatest contemporary musicians entertained at Buckingham Palace. The composer Felix Mendelssohn is known to have played there on three occasions. Johann Strauss II and his orchestra played there when in England. Strauss's "Alice Polka" was first performed at the palace in 1849 in honour of the queen's daughter, Princess Alice. Under Victoria, Buckingham Palace was frequently the scene of lavish costume balls, in addition to the usual royal ceremonies, investitures and presentations.

Now answer this question: Who performed Alice Polka in honor of Princess Alice?

Output: Johann Strauss II

Input: Article: Shorter, black-and-white daily strips began to appear early in the 20th century, and became established in newspapers after the success in 1907 of Bud Fisher's Mutt and Jeff. Humour strips predominated at first, and in the 1920s and 1930s strips with continuing stories in genres such as adventure and drama also became popular. Thin periodicals called comic books appeared in the 1930s, at first reprinting newspaper comic strips; by the end of the decade, original content began to dominate. The success in 1938 of Action Comics and its lead hero Superman marked the beginning of the Golden Age of Comic Books, in which the superhero genre was prominent.

Now answer this question: When did comic books make an appearance?

Output: 1930s

Input: Article: Greater London encompasses a total area of 1,583 square kilometres (611 sq mi), an area which had a population of 7,172,036 in 2001 and a population density of 4,542 inhabitants per square kilometre (11,760/sq mi). The extended area known as the London Metropolitan Region or the London Metropolitan Agglomeration, comprises a total area of 8,382 square kilometres (3,236 sq mi) has a population of 13,709,000 and a population density of 1,510 inhabitants per square kilometre (3,900/sq mi). Modern London stands on the Thames, its primary geographical feature, a navigable river which crosses the city from the south-west to the east. The Thames Valley is a floodplain surrounded by gently rolling hills including Parliament Hill, Addington Hills, and Primrose Hill. The Thames was once a much broader, shallower river with extensive marshlands; at high tide, its shores reached five times their present width.

Now answer this question: What was the population density of Greater London in 2001?

Output:
4,542 inhabitants per square kilometre (11,760/sq mi)