听力原文： Today I would like to demonstrate the tone of different kinds of pianos, to demonstrate how the tone varies according to the shape and how it is placed in a room. Excluding archaic variations of the internal works of the piano, there are basically three kinds of pianos, two of which are in common use today. The first kind, the one you are certainly most familiar with, is the grand. Although there are different sizes of grand piano, some longer and others shorter, they feature horizontally cross-strung strings and a top lid that is usually opened to reflect the sound toward the audience. It achieved its modern form. mostly in order to achieve a full resonance that could fill a large concert auditorium. The square piano is an outdated form. that is no longer manufactured. Its strings are also horizontally strung, but compressed into a much smaller frame, with the keyboard set toward the end of one of the long sides. It was designed to produce a sound like that of the grand piano, but in more functional rectangular shape that would fit bettering the large parlors of nineteenth century houses. However, for reasons of cost and size, they were replaced by the upright piano, whose strings are vertical. As they are placed in most houses, the upright depends more on resonance off an adjacent wall and occupies a minimum amount of space. As you will readily hear, the grand produces a more brilliant sound, though nowadays far more uprights are being sold. What is the main concern of talk?