Which of the following statements is true of early space exploration? A. The first manned space exploration took place in 1957, when the United States launched Sputnik I.
B. The first manned space exploration took place in 1958, when the Soviet Union launched Explorer I.
C. The first manned exploration of space took place in 1961, when NASA's Mercury Project launched the first astronaut into suborbital space.
D. The first manned exploration of space took place in 1961, when the Soviet Union launched Vostok 1.