单项选择题

Fifty years ago, on May 25, 1961, US President John F. Kennedy (31) a grand challenge that changed the world (32) humankind knew it— (33) a man to the Moon and bring him home again, and to do it by the end of the decade.
It is one of the most (34) images of all time an Earthling (35) foot upon the Moon for the first time. The moment was immortalized by astronaut Neil Armstrong. "One small step for a man, one giant (36) for mankind," said Armstrong.
The challenge to put a man on the Moon had been issued on May 25, 1961, by newly elected President John F. Kennedy in a bold speech before Congress. "First, I believe that this nation (37) commit itself to (38) the goal, before this decade is out, (39) landing a man on the Moon and returning him safely to the earth. No (40) space project in this period will be more (41) to mankind, or more important in the long-range exploration of space; and none will be so difficult or expensive to accomplish..." said President Kennedy.
To set the stage for this speech, here is a bit of history: In 1957, the Soviet Union (42) Sputnik—the first (43) object (44) placed into orbit around Earth. And only one month before Kennedy’s speech, the Soviets sent the first man into space, Yuri Gagarin. Three weeks later an American (45) suit—Alan Shepard, who admired the view from his Freedom Seven Mercury space capsule. "On the periscope—what a beautiful view," said Shepard. "Cloud cover over Florida."
The Space Race was well (46) . The Apollo Eleven (47) was the first manned mission to land on the Moon. It was the fifth human spaceflight of Project Apollo and the third human (48) to the Moon. It was also the second all-veteran crew in manned spaceflight history. Launched on July 16, 1969, it carried Mission Commander Neil Alden Armstrong, Command Module Pilot Michael Collins and Lunar Module Pilot Edwin Eugene "Buzz" Aldrin, Jr. On July 20, Armstrong and Aldrin became the first (49) to land on the Moon, while Collins orbited above.
The mission fulfilled President John F. Kennedy’s goal of reaching the moon (50) the end of the 1960s.