Plugin the answers into the sentence to see if it makes sense.
They had been known each other for a long time before they finally decided to get married, it doesn't sound right so you can eliminate that answer and choose the other one.
They had known each other for a long time before they finally decided to get married sounds grammatically correct.
<span>"We had passed through long walls of piled skeletons, with casks and puncheons intermingling, into the inmost recesses of the catacombs." "</span><span>His eyes flashed with a fierce light. He repeated the movement --a grotesque one."
