Final answer:
The verb perder in the present tense is 'pierden' which means 'to lose'.
Step-by-step explanation:
The correct form of the verb perder to fill in the blank in the sentence 'Mis padres siempre. las llaves.' is the present tense form 'pierden'.
Therefore, the sentence should be: 'Mis padres siempre pierden las llaves.'
The verb perder means 'to lose' in English. So the sentence translates to 'My parents always lose the keys.'
Learn more about Spanish verb conjugation