Complex sentence: The Apollo program was the third human spaceflight program carried out by the National Aeronautics and Space Administration (NASA) the United States'civilian space agency, and was the program responsible for the landing of the first humans on Earth's Moon in 1969.
Split into simpler sentences: The Apollo program was the third human spaceflight program carried out by the National Aeronautics and Space Administration (NASA) the United States'civilian space agency. The program was responsible for the landing of the first humans on Earth's Moon in 1969.