3 Do the pairs of sentences mean the same? Mark S for same or D for different. If they are different, can you explain why? 1 a You need to book in advance to get a cheap ticket. b You don't have to buy your ticket in advance, but it costs more on the day. 2 a You don't have to take a lot of cash with you. b It's sensible to take plenty of money with you. 3 a You shouldn't buy tickets on the internet from people you don't know. b It's a bad idea to buy tickets on the internet from people you don't know. 4 a You should try to stay with your friends if there are big crowds. b You have to stay with your friends if there are a lot of people there. 5 a You have to be with an adult if you're under 16, or you can't go in. b People aged under 16 can only go in if they're with an adult. 6 a You don't have to take a phone. b You needn't take a phone. 7 a You should buy travel insurance before you go. b My advice is to buy insurance before you travel. 8 a You need to be at the airport at least two hours before your flight leaves. b The airline says that you must be at the airport two hours before you fly.