Final answer:
The correct expression to complete the sentence is 'Los que.' The sentence translates to 'The waiters are the ones who speak with the customers.'
Step-by-step explanation:
The correct expression to complete the sentence is Los que.
So, the complete sentence would be:
Los meseros son los que hablan con los clientes.
This translates to:
The waiters are the ones who speak with the customers.
Learn more about Completing a sentence in Spanish