電大開放英語2考試小抄-免費閱讀

　　

【正文】 the adoption of an approach to space in which all parts of the canvas played an equally vital role in the total work。 and there are some of each type in the brain. These terms are used because nicotine mimics the action of acetylcholine at nicotinic receptors, whereas muscarine, an alkaloid from the mushroom Amanita muscaria, mimics the action of acetylcholine at the muscarinic receptors. Acetylcholine is the neurotransmitter produced by neurons referred to as cholinergic neurons. In the peripheral nervous system acetylcholine plays a role in skeletal muscle movement, as well as in the regulation of smooth muscle and cardiac muscle. In the central nervous system acetylcholine is believed to be involved in learning, memory, and mood. Acetylcholine is synthesized from choline and acetyl coenzyme A through the action of the enzyme choline acetyltransferase and bees packaged into membranebound vesicles . After the arrival of a nerve signal at the termination of an axon, the vesicles fuse with the cell membrane, causing the release of acetylcholine into the synaptic cleft . For the nerve signal to continue, acetylcholine must diffuse to another nearby neuron or muscle cell, where it will bind and activate a receptor protein. There are two main types of cholinergic receptors, nicotinic and muscarinic. Nicotinic receptors are located at synapses between two neurons and at synapses between neurons and skeletal muscle cells. Upon activation a nicotinic receptor acts as a channel for the movement of ions into and out of the neuron, directly resulting in depolarization of the neuron. Muscarinic receptors, located at the synapses of nerves with smooth or cardiac muscle, trigger a chain of chemical events referred to as signal transduction. For a cholinergic neuron to receive another impulse, acetylcholine must be released from the receptor to which it has bound. This will only happen if the concentration of acetylcholine in the synaptic cleft is very low. Low synaptic concentrations of acetylcholine can be maintained via a hydrolysis reaction catalyzed by the enzyme acetylcholinesterase. This enzyme hydrolyzes acetylcholine into acetic acid and choline. If acetylcholinesterase activity is inhibited, the synaptic concentration of acetylcholine will remain higher than normal. If this inhibition is irreversible, as in the case of exposure to many nerve gases and some pesticides, sweating, bronchial constriction, convulsions, paralysis, and possibly death can occur. Although irreversible inhibition is dangerous, beneficial effects may be derived from transient (reversible) inhibition. Drugs that inhibit acetylcholinesterase in a reversible manner have been shown to improve memory in some people with Alzheimer39。 9) no + 比較級 + than 的結構表示 A 和 B 一樣不 …… 。例如： The car runs faster than 110 miles. 那輛車時速為 110多英里。前一個句型結構表示的意義是 越（怎么樣就）越（怎么樣） ，在這個結構中的兩個 比較級 不要求一定詞性相同，它們各自的詞性要依句子的需要而定；后一個句型結構表示的意義是 越來越（怎么樣） ，在這個結構中的兩個 比較級 則要求詞性相同。 This street is narrower than that one. 這條街比那條街窄一些。 She hasn39。s. 他的寢室沒有他姐姐的整潔。 3) 形容詞的最高級前一般必須有定冠詞 the；但是也有不加定冠詞 the的幾種情況。學習目標：學習與冒險和度假活動相關的詞匯；復習動詞 to get 的用法；學習級別形容詞和極限形容詞；復習過去分詞和現在分詞用作形容詞。另外， every 可用于 [ every other (或 every +數詞 ) + 名詞 ]的結構中，表示 每隔 …… 之意思： every other day 每隔一天 every three years 每隔三年 every third year 每隔三年 every other line 每隔一行 every ten miles 每隔十哩 Unit3136 學習內容及目標 課時分配：布置學習及內容簡介 1 課時；面授 3 課時；答疑解惑 2 課時。 Even if they were to fail, they wouldn39。學習目標：學習描述科技發展的詞匯；復習被動語 態；復習含有情態動詞的被動語態；學習議論文的結構；復習連接詞語的用法。 Unit2530 學習內容及目標 課時分配：布置學習及內容簡介 1 課時；面授 3 課時；答疑解惑 2 課時。 We happened to have e across the article once .我們碰巧有一次見過這篇文章。 What shall we be doing next ? 我們干什么？ If you don39。 What will you be doing tomorrow morning? 明天上午你做什么？ It won39。例如： I may not e to see you recently unless I can plete the project ahead of time .除非我能提前完成那個項目，否則我最近不會來看你了。 在復合賓語結構中，有些動詞如： feel , hear , notice see , watch 等后面既可以用現在分詞作賓語補足語，也可用不帶 to的不定式來充當。 My sister was heard singing that song in English outside. （主語補足語）有人聽到我妹妹在外面用英文唱那首歌。例如： The game being over, the audience stood up and cheered for the winner. （表示時間）比賽結束時，觀眾站起來為勝者歡呼。 另外， 若想明確表示分詞動作發生在謂語動作之前，可用分詞的完成形式（其中包括主動式和被動式）： Having + 過去分詞 （主動式）， Having + been + 過去分詞 （被動式）。 Laughing and talking loudly, the audience left the stadium after the match. （表示伴隨性的方式）比賽結束后，觀眾們大聲說著，笑著離開了賽場。也就是說，我們總是選一個最重要的動作為句子的謂語，而把其它的次要動作寫成分詞形式。 She looked disappointed after she lost the game. 輸掉那場比賽后，她看上去很失望。 另外，分詞作定語還有 being + 過去分詞 的形式。 1）作定語 單個分詞作定語，分詞一般說來寫在被修飾的名詞、代詞之前；分詞短語作定語時，分詞放在被修飾詞之后。 Mother heard the door opened . 媽媽聽見門打開了。 現在我們用實例來說明分詞的這兩大區別。 分清現在分詞與過去分詞的區別是我們決定用何詞形式的重要依據。因此，在討論分詞的句法作用之前，讓我們先討論一下這兩個概念問題。學習目標：學習與語言相關的詞匯；學習不定式的進行式； be going to 表示預測；復習 so 的用法；復習將來完成時； likely, probably 和 possibly 的用法。課時分配：布置學習及內容簡介 1 課時；面授 3 課時；答疑解惑 2 課時。 第 23 單元 在本單元中，你將學習了解世界媒體是如何 報導新聞的。 這里所說的 分詞的動作意義 是指拋開它的形式，只談 動作表達的意思 。下面我們看看這兩種分詞形式的區別： 現在分詞 : 1）分詞和與其相關的名詞、代詞之間構成 一種 主謂關系 ，即 主動態 。 例一 I don39。 例二 China belongs to developing countries . 中國屬于發展中國家。 現在分詞作定語，主要說明 正在進行的動作 或是 一個在現在或過去某段時間內的經常化動作 。這種表達形式的意義是 分詞動作正在進行；但分詞動作與其所修飾的詞之間是動賓關系 。 What he said sounds convincing. 他的話聽起來很有說服力。 上述的情況也可視為使用分詞作狀語的前提條件。 Surrounded by his students , the professor sat there cheerfully . （表示伴隨 性的方式）那位教授在學生們的簇擁下，興高采烈地坐在那兒。 分詞作狀語還有 being + 過去分詞 的形式。 The decision having been made, they began to think of how to carry it out . （表示時間）決議已經作出，他們開始考慮 怎樣執行它。 They once heard the song sung in English. （賓語補足語）他們曾聽見有人用英文唱那首歌。但這兩種情況在表達的意義上有所不相同：用現在分詞作賓語補足語，強調分詞動作在發生和進行之中；用不帶 to的不定式來充當賓語補足語，則著重說明不定式動作從發生到結束的全過程。或者：除非我能提前完成那個項目，我最近才會來看你了。t be long before that we will be making a new puter for more advanced calculation. 不久我們就要造一部新計算器進行更高級的運算。t do so , you will be facing great difficulties. 你如果不這樣做就會面臨很大的困難。 不定式的 完成式 則表示不定式的動作業已發生 ，并 發生于謂語動作之先 。