David R. Scott and James B. Irwin, the pilot of Falcon, began history's first drive on the moon after unfolding the Lunar Roving Vehicle (LRV) from Falcon and setting it up. The ability of the Apollo 15 astronauts to explore the moon's surface was significantly enhanced by the use of the LRV. During three separate motor trips, they explored the rim of Hadley Rille, the edges of deep craters, and the slopes of the Apennine Mountains. At a number of science stops, the astronauts turned on the LRV color television camera enabling viewers throughout the world to observe such spectacular vistas as the canyon depths of Hadley, the undulating, crater-scarred plain of the Marsh of Decay, and the rounded peaks of the towering Apennines.

Q. Underline the topic sentence.