Final answer:
The appropriate interrogatory word for the blank in the dialogue is 'Dónde'.
Step-by-step explanation:
The appropriate interrogatory word for the blank in the dialogue is Dónde. The student is asking 'vamos al restaurante?' which means 'are we going to the restaurant?'. In response, the person says 'vamos a las slete y media' which means 'we are going at seven thirty'. To ask 'where' they are going, the correct question would be '¿Dónde vamos?'
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