21* Choose the correct response.A: Can I have a ticket to London, please?B: a Certainly. Single or return?b Single, please2A: Thank you for your help.B: a Thank you. b You're welcome3A: That's £95, please.B: a Here you are. b You're welcome.4A: Can you tell me which platform it leavesfrom?B: a The 16:35 train.b It leaves from platform 4.