Task: Question Answering
Input (English): Passage: The Monadnock was commissioned by Boston real estate developers Peter and Shepherd Brooks in the building boom following the Depression of 1873–79. The Brooks family, which had amassed a fortune in the shipping insurance business and had been investing in Chicago real estate since 1863, had retained Chicago property manager Owen F. Aldis to manage the construction of the seven-story Grannis Block on Dearborn Street in 1880. It was Aldis, one of two men Louis Sullivan credited with being "responsible for the modern office building", who convinced investors such as the Brooks brothers to build new skyscrapers in Chicago. By the end of the century, Aldis would create over 1,000,000 square feet (93,000 m2) of new office space and manage nearly one fifth of the office space in the Loop.Daniel Burnham and John Wellborn Root met as young draftsmen in the Chicago firm of Carter, Drake, and Wight in 1872 and left to form Burnham & Root the following year. At Aldis's urging, the Brooks brothers had retained the then-fledgling firm to design the Grannis Block, which was their first major commission. Burnham and Root would become the architects of choice for the Brooks family, for whom they would complete the first high-rise building in Chicago, the 10-story Montauk Building, in 1883, and the 11-story Rookery Building in 1888.
The Great Chicago Fire of 1871 had destroyed a 4-mile (6.4 km) by 0.5-mile (0.80 km) swath of the city between the Chicago River and Lake Michigan, and subsequent commercial development expanded into the area far south of the main business district along the river that would come to be known as "the Loop". Between 1881 and 1885, Aldis bought a series of lots in the area on Peter Brooks' behalf, including a 70-by-200-foot (21 by 61 m) site on the corner of Jackson and Dearborn streets. The location was remote, yet attractive for several reasons. The construction of the Chicago Board of Trade Building in 1885 had made nearby LaSalle Street the city's prime financial district, driving up property values, and railroad companies were buying up land further south for new terminal buildings, creating further speculation in the southeastern end of the Loop. Brooks commissioned Burnham & Root to design a building for the site in 1884, and the project was announced in 1885, with a brief trade journal notice that the building would cost $850,000 ($23.7 million in 2018 dollars). The Chicago building community had little faith in Brooks' choice of location. Architect Edwin Renwick would say: When Owen Aldis put up the Monadnock on Jackson Boulevard there was nothing on the south side of the street between State Street and the river but cheap one-story shacks, mere hovels. Every one thought Mr. Aldis was insane to build way out there on the ragged edge of the city. Later when he carried the building on through Van Buren Street they were sure he was. 
Question: What firm's first major commission was the Grannis Block?
Output (English): Burnham & Root.