Final answer:
In the sentence 'The friends laughed ___ their terrible luck,' the correct preposition to use is 'at,' making the complete sentence: 'The friends laughed at their terrible luck.'
Step-by-step explanation:
The correct preposition to complete the sentence "The friends laughed ___ their terrible luck." is 'at.' Therefore, the completed sentence should read: "The friends laughed at their terrible luck." The preposition 'at' is used to point towards the object of the laughter, in this case, the 'terrible luck' that the friends are experiencing.
This usage is consistent with expressing a reaction towards something ironic or unexpected, which is common in English literature and everyday speech.
The correct preposition to fill in the blank in the given sentence is 'at.' The phrase 'laugh at' is commonly used to express amusement or ridicule towards someone or something. In this case, the friends are laughing at their terrible luck.