问题 选择题

变形虫(一种单细胞的动物)的细胞结构与植物细胞不同的是没有(  )

A.细胞质

B.细胞膜

C.细胞壁

D.细胞核

答案

植物细胞的结构包括细胞壁、细胞膜、细胞质、细胞核、液泡、叶绿体、线粒体等;变形虫是原生动物,其细胞结构中没有细胞壁、液泡和叶绿体,变形虫之所以能改变形状,是因为细胞膜没有细胞骨架,即膜骨架,使细胞不能维持一定的形态,因此变形虫有伸出伪足的能力,造成细胞质流动,使形态不固定.因此变形虫与植物细胞不同的结构是细胞膜.

故选:C

填空题
单项选择题

WWW is popular for its multimedia transmission and friendly (71) . Although the speed of network has been improved considerably in recent years, the rapid (72) of using the Internet, the inherited character of delay in the network and the Request/Response working mode of WWW still make the Internet traffic very (73) and give no guarantee on the Quality of Service. Because HTTP has no states, the web server cannot know the users’ demand and the users’ requests cannot be predicted Taking advantage of a cache mechanism and the time locality of WWW accesses, the browser can preserve the documents ever accessed in the local machine. By this means, for the documents in the local cache, the browser does not need to send the requests to the remote server or to receive the whole responses from the remote one Pre-fetching uses the space locality of accesses First, the users’ access requests are predicted according to the users’ current request. Secondly, the expected pages are fetched into the local cache when the user is brow sing the current page. Finally, the users can access these pages downloaded from the local cache. And this can reduce the access delay to some degrees. Pre-fetching is one kind of active caches that can cache the pages which are still not requested by the user. The application of pre-fetching technology in the web can greatly reduce the waiting time after users have sent their requests. This paper brings forward an intelligent technique of web pre-fetching, which can speed up fetching web pages. In this technique, we use a simplified WWW data model to represent the data in the cache of web browser to mine the association rules. We store these rules in a knowledge base so as to (74) the user’s actions. In the client sides, the agents are responsible for mining the users’ interest and pre-fetching the web pages, which are based on the interest association repository. Therefore it is (75) for the users to speed up the browsing.

(75)处填()。

A.transparent

B.clear

C.fuzzy

D.changeable