According to the author, what is the impracticability of using coal, oil shale and coal tars' as sources of energy due to?Đoạn văn30/30According to the author, what is the impracticability of using coal, oil shale and coal tars' as sources of energy due to?They take a lot of time They are expensiveThey are non-renewable resources They are scarce resourcesGiải thíchChọn đáp án B