Zero conditional When we talk about things that are generally or always true, we can use: If/When/Unless plus a present form PLUS present simple or imperative If he gets there before me, ask him to wait. When you fly budget airline, you have to pay for your drinks and snacks. Unless you need more space, a small car is big enough for one person. Note that we are not talking about a specific event but something which is generally true. In the condition clause, we can use a variety of present forms. In the result clause, there can only be the present simple or imperative. If you visit London, go on the London Eye. If unemployment is rising, people tend to stay in their present jobs. If you've done that, go and have a coffee. When you go on holiday, take plenty of sun cream. It'll be very hot. When I'm concentrating, please don't make so much noise. When I've finished an article, I always ask Kate to read it through. Notice that 'unless' means the same as 'if not'. Unless he asks you politely, refuse to do any more work on the project. Unless prices are rising, it's not a good investment. Unless you've been there yourself, you don't really understand how fantastic it is. Exercise If you see him , tell him I want to speak to him. If you get there early, wait for me in the hall. If you receive it tomorrow, give me a call. When you buy on-line, you save ten percent. When you fly on one of the budget airlines, you have to buy snacks. When you do exercise , drink plenty of water. Unless you pay extra, you get the basic service. Unless he is going to pay you , don't do it. Unless I phone to say I will be late, expect me at 8 o' clock. When you go to London , try some of the specialities in the typical restaurant. If you are going , pick me up on the way. If you have finished all your work , go home early. When he get there, don't say anything to him , I want to keep it secret. Don't talk about things like that when we are having lunch. When you have painted the kitchen , you can paint the wall. I will give you a call when I am ready to leave. If you are thinking of going to Paris, talk to Jhon, he knows it well. When I am speaking on the phone, please don't make so much noise. If it is raining , take a taxi. If , when or unless. Take the train unless they are on strike again. If you see them ,say hello from me . When you have finished with it , bring it back. If you can't find yours, use mine. It's not worth buying, unless the house price are rising quickly. Come with me, unless you have something better to do. If he asks you again, say no. If you want to get there on time, the best thing is to take the train. When you are reading a foreign language , don't translate . 本文来源：https://www.wddqw.com/doc/bcb5f6d3240c844769eaeed4.html