在计算机中，数据输入输出的控制方式有多种，“中断”方式的优点不包括（）。 A．I/O

Ragtime is a musical form that synthesizes folk melodies and musical techniques into a brief quadrille-like structure, designed to be played--exactly as written--on the piano. (46) A p analogy exists between European composers like Ralph Vaughan Williams and Edward Grieg, who combined folk tunes and their own original materials in larger compositions and the pioneer composers in the United States. Composers like Scott Joplin and James Scott were in a sense collectors or musicologists, collecting dance and folk music in Black communities and consciously shaping it into brief suites or anthologies called piano rags.

It has sometimes been charged that ragtime is mechanical. For instance, Wilfred Mellers comments, "rags were transferred to the pianola roll and, even if not played by a machine, should be played like a machine, with meticulous precision. " (47) However, there is no reason to assume that ragtime is inherently mechanical simply because commercial manufacturers applied a mechanical recording method to it, the only way to record pianos at that date. Ragtime’s is not a mechanical precision, and it is not precision limited to the style of performance. It arises from ragtime’s following a well-defined form and obeying simple rules within that form.

The classic formula for the piano rag disposes three to five themes in sixteen-bar strains, often organized with repeats. (48) The rag opens with a bright, memorable strain or theme, followed by a similar theme, leading to a melody of marked lyrical character, with the structure concluded by a lyrical strain that parallels the rhythmic developments of the earlier themes. The aim of the structure is to rise from one theme to another in a stair-step manner, ending on a note of triumph or exhilaration. Typically, each strain is divided into two 8-bar segments that are essentially alike, so the rhythmic-melodic unit of ragtime is only eight bars of 2/4 measure. (49) Therefore, not concerned with development of musical themes, the ragtime composer instead sets a theme down intact, in finished form, and links it to various related themes that are brief with clear melodic figures. Tension in ragtime compositions arises from a polarity between two basic ingredients: a continuous bass--called by jazz musicians a boom-chick bass--in the pianist’s left hand, and its melodic, syncopated counterpart in the right hand. Ragtime remains distinct from jazz both as an instrumental style and as a genre. Ragtime style stresses a pattern of repeated rhythms, not the constant inventions and variations of jazz. (50) As a genre, ragtime requires strict attention to structure, not inventiveness or exceptional skills, existing as a tradition, a set of conventions, a body of written scores, separate from the individual players associated with it. In this sense ragtime is more akin to folk music of the nineteenth century than to jazz.

(48) The rag opens with a bright, memorable strain or theme, followed by a similar theme, leading to a melody of marked lyrical character, with the structure concluded by a lyrical strain that parallels the rhythmic developments of the earlier themes.

地衣是植物界中结构奇特、与众不同的一个大家族，它分泌的地衣酸可腐蚀岩石。对土壤的形成起着开拓作用，堪称不毛之地的“拓荒先锋”。
长期以来，地衣的结构都是不解之谜。直到1867年，德国植物学家西蒙·释义德奈尔才揭示了它的奇特结构——地衣是由两种截然不同的生物(藻类和真菌)高度结合而成的复合体。在这个复合体内，真菌的菌丝缠绕藻细胞，并包围藻类，夺取藻类光合作用制造的有机物，使藻类与外界隔绝，只能靠真菌供给水分、CO2和无机盐。有些地衣中的真菌还可以分泌出一种物质来溶解岩石，释放出地衣生长所需要的无机物。若二者分离，藻类能生长、繁殖，而真菌就会饿死。可见，它们是在弱寄生基础上发展起来的一种利益不均等的特殊共生关系，这种关系已经存在了近7000万年，是目前生物界共生关系最成功的典范。但科学家们至今也没有完全弄明白其共生原因。
众所周知，乌龟长寿的秘诀在于新陈代谢缓慢。同样的，地衣长寿的诀窍也是生长极其缓慢。据观察，地衣在一年中也许只有一天的活跃生长期。因此，科学家们认为，南极那些直径已经长到13厘米的地衣可能是地球上活着的最为古老的生物!而在离南极点只有483千米的一些山峰上，人们也发现了生长得很好的地衣，也就是说，地衣是地球上生长的最靠南的植物。
地衣在全世界有500余属2万多种。地衣具有极为顽强的生命力。在我们周围的树干和土壤上，或者是裸岩悬壁中，甚至是高山、极地和沙漠里都有地衣的踪迹。实验证明，地衣能忍受70℃左右的高温而不死亡，在-268℃的低温下放几个小时仍能恢复正常生长。[ ]，地衣恐怕也是地球上最为耐寒的植物。[ ]在博物馆的陈列柜里放了15年的地衣，沾上水之后，居然还能“死”而复生。
地衣靠孢子来繁殖。孢子来自地衣中的真菌，而藻类不参与生殖。孢子飘浮在空气中，遇到合适的环境，就会萌发产生新个体，当遇到合适的藻类细胞时，它们又结合起来继续生长。另一种繁殖方式是地衣上出现“芽体”，这种芽体实际上是几个藻细胞被菌丝裹住，随风飘散，到达适宜的环境里，又可长出新的地衣体。地衣的生长慢得惊人，但寿命很长。人们发现北极岩石上的一小块地衣已有数百岁，而且还将长期存活。
在大城市虽然很少见到地衣，但它其实并不陌生，我们最熟悉的酸碱指示剂“石蕊试液”或“石蕊试纸”就是从地衣中提取的。此外，地衣还应用于许多方面：①药用，②食用、动物饲料，③配制化妆品、香水、香皂等，也可用于卷烟；有的可作染料、指示剂等。
不过地衣也有害处。它能寄生在经济树木，特别是柑橘、茶树上，是寄生虫的藏身地；森林中的云杉、冷杉也挂满地衣，因为它的覆盖影响了光照和呼吸。某些壳状地衣还会生长在古老的玻璃窗上，影响室内光线。因此，我们在利用地衣的同时，还要防止它的危害。

对划线句“但科学家们至今也没有完全弄明白其共生原因”的理解正确的是( )。

A．科学家不知道地衣是藻类和真菌类两种物质的共生

B．科学家们对地衣的研究领域相对比较狭小

C．科学家们对地衣共生的原因了解一些

D．科学家们完全不了解地衣共生的原因

、的同分异构体中，某苯环上的一氯代物只有一种的结构有（不考虑立体异构）

A．6种

B．5种

C．4种

D．3种

深基坑安全专项施工方案论证报告作为对所论证深基坑安全专项施工方案修改完善的（）意见。

A.参考

B.指导

C.最终

D.决定

（）是指在较短时间内突然爆发的，群体与群体之间、群体与领导之间、群体与企事业单位之间的，以经济利益为主要内容的，采取围攻、静坐、游行、集会等方式对抗党政机关甚至破坏社会公共财物、危害干群人身安全、扰乱社会秩序的事件。

A、突发性事件

B、群体事件

C、突然性事件

D、突发性群体事件