WHAT IS THE TONE OF THE PASSAGE

9. - File thứ 1: De va dap an thi thu lan 2, Anh
Tiếng Anh File thứ 1: De va dap an thi thu lan 2, Anh
9. What is the tone of the passage? A. A biased representation of the development of helicopter flight. B. A comparison of helicopters and fixed wing aircraft. C. A personal account of helicopter development. D. An impartial overview of the development of helicopters.