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29、志愿服务的精神是（ ）
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30、职业生活中的道德和法律有许多共同的特点，包括（ ）
Rock and roll is a genre of popular music that evolved in the United States in the late 1940s and early 1950s. It’s __1__ lie mainly in blues, rhythm and blues, country, folk, gospel, and jazz. The style subsequently spread to the rest of the world and developed further, leading ultimately to __2__ rock music.The term “rock and roll”now covers at least two different meanings, both in common usage. The American Heritage Dictionary and the Merriam Webster Dictionary both __3__ rock and roll as synonymous with rock music.__4__, Allwords.com defines the term as referring specifically to the music of the 1950s.Classic rock and roll is __5__ played with one or two electric guitars, a string bass or an electric bass guitar, and a drum kit. In the __6__ rock and roll styles of the late 1940s, either the piano or saxophone was often the lead instrument, but these were generally __7__ or supplemented by the guitar in the middle to late 1950s.The massive popularity and eventual world view of rock and roll gave it a __8__ social impact. Far beyond simply a musical style, rock and roll, as seen in movies and in the new medium of television, __9__ lifestyles, fashion, attitude, and language. It went on to spawn various sub-genres, often without the initially __10__ backbeat, that are now more commonly called simply “rock music”or “rock”.A.define B. characteristic C. unique D. rootsE. usually F.Basically G. earliestH.influencedI.followedJ.modernK.explanation L.Conversely M.replaced N.prepare O.seldom
只要保证比特信噪比大于1.42dB，不断增大MFSK的进制数就能使得MFSK信号的误码率达到任意小.
同样的码元速率下，为得到同样的误码率多电平MASK调制需要比2ASK更高的信噪比。
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