Renewable Energy and Fossil Fuels. Past Tenses

Choose the correct option. The government __________ to replace coal with renewable energy sources for years before the policy finally took effect.

Choose the correct option. Engineers __________ the old turbine before they replaced it with a more efficient one.

Choose the correct option. By the time scientists discovered the extent of pollution, fossil fuel companies __________ significant amounts of carbon dioxide into the atmosphere.

Choose the correct option. While engineers __________ the turbine, they found a problem with its design.

Choose the correct option. Renewable energy sources _______ much more popular by the time fossil fuel prices rose dramatically.

Open the brackets and write the correct answer. As the sun was setting, the wind turbines __________ (generate) power continuously.

Open the brackets and write the correct answer. Before the plant closed, it __________ (release) thousands of tons of carbon dioxide into the atmosphere.

Open the brackets and write the correct answer. By the time renewable energy options became widespread, scientists already __________ (study) the environmental impact of fossil fuels for decades.

Open the brackets and write the correct answer. Fossil fuels __________ (pollute) the air long before renewable energy was considered a feasible alternative.

Open the brackets and write the correct answer. While they __________ (test) the new turbine, they noticed it could convert energy much more efficiently.