（46）"Popular art" has a number of meanings, impossible to define with any precision, which range from folklore to junk, with poles being clear enough but the middle tending to blur. The Hollywood Western of the 1930’s, for example, has elements of folklore, but is closer to junk than to high art or folk art. There can be great trash, just as there is bad high art. The musicals of George Gershwin are great popular art, never aspiring to high art. Schubert and Brahms, however, used elements of popular music--folk themes--in works clearly intended as high art. The case of Verdi is a different one : he took a popular genre-- bourgeois melodrama set to music (an accurate definition of nineteenth-century opera)- and, without altering its fundamental nature, transmuted it into high art. (47) This remains one of the greatest achievements in music, and one that cannot be fully appreciated without recognizing the essential trashiness of the genre.
As an example of such a transmutation, consider what Verdi made of the typical political elements of nineteenth-century opera. (48) Generally in the plots of these operas, a hero or heroine--usually portrayed only as an individual, unrestrained by class--is caught between the immoral corruption of the aristocracy and the doctrinaire rigidity of the leaders of the civilians. Verdi transforms this naive and unlike formulation with music of extraordinary energy and rhythmic vitality, music more subtle than it seems at first hearing. There are scenes and arias that still sound like calls to arms and were clearly understood as such when they were first performed. Such pieces lend an immediacy to the otherwise veiled political message of these operas and call up feelings beyond those of the opera itself.
Or consider Verdi’ s treatment of character. (49) Before Verdi, there were rarely any characters at all in musical drama, only a series of situations which allowed the singers to express a series of emotional state. Any attempt to find coherent psychological portrayal in these operas is misplaced ingenuity. The only coherence was the singer’ s vocal technique: when the cast changed, new arias were almost always substituted, generally adapted from other operas. Verdi’ s characters, on the other hand, have genuine consistency and integrity, even if, in many cases, the consistency is that of pasteboard melodrama. The integrity of the character is achieved through the music: (50) once he had become established, Verdi did not rewrite his music for different singers or allow alterations or substitutions of somebody else’s arias in one of his operas, as every eighteenth-century composer had done. When he revised an opera, it was only for dramatic economy and effectiveness.
(50) once he had become established, Verdi did not rewrite his music for different singers or allow alterations or substitutions of somebody else’s arias in one of his operas, as every eighteenth-century composer had done.
，当升降机突然处于完全失重状态时，则此瞬时AB两物体的瞬时加速度为别为（ ）
、
B．
、
D．
，由于失重时A物体本身重力不变，故在此瞬间，A同时受到弹簧的弹力（
，故其瞬时加速度为
；而对B受力分析可知，完全失重瞬间，B受到弹簧的作用总和细线的上弹力相等（此二力的合力为0），则此时B的合力就是其重力，所以B的瞬时加速度为
，所以D正确。