第1个回答 2011-04-13
1, Yet and already are both used when talking about the possible completion of an action by or before a particular time. They are mostly used with the perfect tenses (in US usage also with the simple past). *yet和already均用以表示到某时或某时前可能完成的动作. 两者多与完成时态连用(在美式英语中还与简单过去时态连用). Yet is only used in negative statements and in questions *yet只用於否定的陈述句及疑问句: `It's time to go. ' `I'm not ready yet.' ‘该走了.’‘我还没准备好呢.’ * Are you out of bed yet? 你已经起床了吗? Already emphasizes the completion of an action. It is usually used in positive statements*already强调动作的完成, 常与肯定的陈述句连用: By midday they had already travelled 200 miles. 到中午为止, 他们已经走了200英里了. Already can be used in questions to express surprise *already可用於疑问句, 表示惊奇: Have you finished lunch already? It's only 12 o'clock! 你已经吃过午饭了吗? 现在才12点钟啊!
2,A.has been on 现在完成时表示过去进行了一段时间且还有可能继续下去,这里for ten minutes是一段时间电影肯定还会继续的,所以A要用has been on
B. is, started. 本来用since引导从句时,主句是要用完成时的,但一种特殊情况除外,就是这里主句是表示一段时间,则主句可用现在完成时,也可以用一般现在时,就是说这里可以填has been,也可以填is,但既然只有一空,当然填is了;至于第二空,应该没什么疑问吧,“电影开始”是过去发生的一件事,用一般过去时