WHAT IS THE TOPIC OF THE PASSAGE

43. - 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
43. What is the topic of the passage? A. Aircraft design in the 20th century. B. The invention of the swash plate. C. The development of the helicopter. D. Which aircraft was the first to fly.