Đọc đoạn văn và khoanh các câu đúng. Bổ sung câu 2 còn thiếu: 24. According to the author, what is the impracticability of using coal, oil shale and coal tars' as sources of energy due to? a. They take a lot of time b. They are expensive c. They are non-renewable resources d. They are scarce resources
