| 词组 | when |
| 释义 | when ◊ used in questions You use when to ask about the time that something happened or will happen. When did you arrive? When are you getting married? 'I have to go to Germany.' ---'When?' ---'Now.' ◊ used in time clauses You use when in time clauses to say that something happened, happens, or will happen at a particular time. He left school when he was eleven. When I have free time, I always spend it fishing. If you are talking about the future, you use the simple present tense in the time clause, not a future tense. When you arrive in Britain, you will have to pass through immigration control. Stop when you feel that your muscles have had enough. ◊ 'when' and 'if' Do not confuse when with if. You use if to mention an event or situation that might happen. You use when to mention something that you expect to happen. For example, if you say 'When we buy a new car, you must come for a drive', you have decided that you are going to buy a new car. If you say 'If we buy a new car, you must come for a drive', you are still undecided about whether or not to buy a car. ◊ 'when', 'as', and 'while' If you want to say what was happening at the time that an event occurred, you can begin by saying what was happening, then add a clause beginning with when. I was just going out when there was a knock at the door. I was watching him go when Joey Morphy came into the alley. You can also use as or while to say what was happening when an event occurred. However, when you use one of these words, you describe the event in the main clause and say what was happening in the clause beginning with as or while. As I was walking one day in Hyde Park, I noticed two elderly ladies. While I was standing outside Woolworth's, I saw Jeremy. If you want to say that two events are continuing to happen at the same time, you usually use while. What were you thinking about while I was getting the drinks? I disliked the noise of football while I was working. ◊ used in non-finite clauses When is sometimes used in non-finite clauses -- that is, in clauses containing an infinisomething belongs to or is connected with. Whose is used in both defining and non-defining clauses. A noun group containing whose can be the subject or object of a verb, or the object of a preposition. When it is the object of a preposition, the preposition can come at lause containing when and a participle. For example, instead of writing 'I often read a book when I am travelling by train', they write 'I often read a book when travelling by train'. Adults sometimes do not realize their own strength when dealing with children. Two other important matters must be considered by anglers when deciding where to fish. Similarly, instead of writing 'When he is interrupted, he gets very angry', someone might write 'When interrupted, he gets very angry'. Michael used to look hurt and surprised when scolded. ◊ used with prepositional phrases and adjectives In writing, when is sometimes not followed by a clause at all, but by a prepositional phrase or an adjective such as 'necessary' or 'possible'. For example, instead of writing 'When you are in Paris, you should visit the Louvre', you might write 'When in Paris, you should visit the Louvre'. When under threat, man reverts with terrifying ease to his primitive past. She had spoken only when necessary. Fresh yeast can be used when available. ◊ used in relative clauses When is often used in non-defining relative clauses. I want to see you at 12 o'clock, when you go to lunch. The Fleishers arrived on a Wednesday, when I was alone. When can also be used in defining relative clauses after 'time' or after a word such as 'day' or 'year'. There had been a time when she thought they were wonderful. This is the year when the profits should start. For information about defining and non-defining clauses, see entry at ↑ ◊ used with 'why' When has a special use which is not related to time. You can add a clause beginning with when to a question which begins with 'why'. You do this as a way of expressing surprise or disagreement at something that someone has said. The 'when'-clause indicates the reason for your surprise or disagreement. Why should he do me an injury when he has already saved my life? Why worry her when it's all over? |
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