Объяснение:

1. By the time we arrived, the construction workers had already set up the scaffolding for the new building.
2. The archaeologists had been digging up artifacts for several months before they made their groundbreaking discovery.
3. The company had been struggling for years before the new CEO took over and implemented changes.
4. The fire department had set off the alarm as soon as they realized there was a gas leak.
5. The residents had been complaining about the noise pollution for weeks before the city council finally put off the construction of the new highway.
6. The forest had been slowly dying out due to the effects of climate change, and conservation efforts were urgently needed.