Open the brackets and write the sentence using the Present Perfect or the Past Simple. ... (they/sell) their house yet?

The sentence requires the Present Perfect tense because of the word "yet", indicating an action that may or may not have happened up to the present moment. The structure for the Present Perfect with 'they' is 'have' + past participle. The past participle of 'sell' is 'sold'. Therefore, the correct form is 'Have they sold their house yet?'.

Answer: Have they sold their house yet?