Directions: The first and the last sentences of the passage are numbered 1 and 6, respectively. The rest of the passage is split into four parts named A, B, C and D. These four parts are not given in their proper order. Read the sentences and find out which of the following combinations is correct.

1. The Wright brothers, Orville and Wilbur, were two American brothers, inventors and aviation pioneers who are credited with inventing and building the world's first successful airplane and making the first controlled, powered and sustained heavier-than-air human flight on December 17, 1903. A. This method became standard and remains standard on fixed-wing aircraft of all kinds. B. In the two years afterwards, the brothers developed their flying machine into the first practical fixed-wing aircraft. C. From the beginning of their aeronautical work, the Wright brothers focused on developing a reliable method of pilot control as the key to solving the flying problem. D. The brothers' fundamental breakthrough was their invention of three-axis control, which enabled the pilot to steer the aircraft effectively and to maintain its equilibrium.
2. This approach differed significantly from other experimenters of the time who put more emphasis on developing powerful engines.