现在完成时讲解 2020-2021学年外研版英语八年级下册

现在完成时 1.含有already,just,yet等的现在完成时 just表示“刚刚”，already表示“已经”，两者都用于肯定句中，一般是置于have/has之后。 yet表示“还未”，有“以后可能会”的含义，用于否定句和疑问句中，一般是置于句末。 Practice Complete the news with already, just and yet. Spaceship on Mars Astronauts have __________ been to the moon but they have not been to any other planets. However, a spaceship has __________ arrived on Mars and it has ________ sent back photos of the red planet. Is there life on Mars? We do not know ______. already already just yet 2.现在完成时和一般过去时的区别 ①两者都表示发生在过去的动作，现在完成时强调过去的动作对现在的影响，而一般过去时则强调是在过去发生的动作这个事实。 ②两者都表示从过去开始并延续了一段时间的动作，现在完成时表示该动作持续到现在，而一般过去时则说明该动作现已终止。 eg:He has lived in Beijing for 4 years. He lived in Beijing for 4 years. 动作仍在继续 动作已结束 3.现在完成时的用法 现在完成时可以表示从过去某一时间开始并持续到现在的动作或状态，一般和表示一段时间的时间状语连用，句中的谓语动词须是延续性动词。这类时间状语通常由for或since引导。 4.含for和since引导的时间状语和现在完成时的区别 ①since表示“自从过去某一时间以来”，后面接表示时间的词、短语或句子，强调动作或状态一直延续到现在，也可以接一般过去时的句子；since多接时间点。 ②for表示时间的延续，后接一段时间。 Complete the sentences with the expressions in the box. have / has been have / has gone 1. A spaceship __________ to Mars. It is coming back to the earth next year. 2. Lots of astronauts ___________ to the space station. They found it very interesting. 3. Some astronauts ____________ to the moon twice. 4. Two British astronauts __________ to the space station. They will come back in January. has gone have been have been have gone 4 Complete the conversation with the correct form of the verbs in brackets. Nicky: I’ve just (1) ________ (watch) a great TV programme about space. Did you know that scientists have (2) _________ (discover) water on Mars? Bill: Yes, I did. And scientists (3) __________ (try) to find life on Mars now. Nicky: Yes, they’re looking for life but they (4) ____________ (not find) anything yet. watched discovered are trying haven’t found Complete the conversation with the correct form of the verbs in brackets. Nicky: I’ve just (1) ________ (watch) a great TV programme about space. Did you know that scientists have (2) _______