Final answer:
Recent Soviet achievements in space motivated Kennedy to prioritize the U.S. space program.
Step-by-step explanation:
Based on President Kennedy's Urgent Message to Congress, recent Soviet achievements in space mostly motivated Kennedy to prioritize the U.S. space program (a). After the Soviets launched Sputnik in 1957 and Yuri Gagarin became the first human to orbit the Earth, Kennedy urged Congress to put a man into space and land an American on the moon. This led to the establishment of NASA and the eventual accomplishment of Kennedy's goal in 1969 when American astronauts landed on the moon.