( ) They were about to leave the house when they heard a fire alarm screaming behind them.

原句“They were about to leave the house when they heard a fire alarm screaming behind them.”可译为： “他们正要离开房子，突然听到身后的火警警报声尖锐地响起。” 核心在于“were about to... when...”结构，表示“正要……这时……”，“screaming”可译为“尖锐地响起”或“刺耳地鸣叫”。综合分析，该句需体现时间上的突然性及“screaming”的拟声效果。 答案：他们正要离开房子，突然听到身后的火警警报声尖锐地响起。