Directions: In the following sentence, there are three underlined parts labelled as (a), (b), and (c). Read the sentence to determine if there is an error in any of the underlined parts. If you find an error, indicate your response on the answer sheet with the corresponding letter (a), (b), or (c). If you do not find any errors, your response should be indicated as (d).

While renewable energy sources such as solar and wind had been gaining popularity, (a) / fossil fuels (b) / still provide the majority of the world's energy. (c) / No error (d)