The answer to this question is B. The other answers are meant to confuse you because two of the people mentioned were astronauts and the other was famous in another way.
Answers A and C are close to being right, but are not actually right. Buzz Aldrin was the second American to walk on the moon. Michael Collins was a US astronaut who was on the mission with Armstrong and Aldrin. However, he did not actually come down to the moon's surface. Instead, he stayed in orbit around the moon, piloting the mission's command module.
Armstrong became famous for being the first man on the moon and for saying of his first step
That's one small step for man, one giant leap for mankind.