i need a train to cambridge on saturday i need to leave london liverpool street sometime after 17:45 .
okay , where are you leaving from ?
{'service': 'train', 'act': 'inform', 'slot_name': 'choice', 'value': 'three'} {'service': 'train', 'act': 'request', 'slot_name': 'arrive', 'value': '?'}
i have 3 options for you , is there a particular time you would like to arrive by ?