The correct answer is "somos seis personas", which means: we are six people. The question "¿Cuántas personas viven en tu casa?" means "How many people live in your house?", so <u>the correct answer must be a number of people</u>. The three other options presented all start with an affirmation "sí", or a refutation, "no". They're all incorrect as the question is not inquiring anything that can be answered with yes or no.
