Write the correct form or tense of the verbs in brackets.
46. Apollo 11 was the first manned mission (land) ……………………on the Moon.
47. A total of six US missions (land) ……………………men on the lunar surface by the end of 1972.
48. In 22 years, Columbia (fly) ……………………27 space flights before disaster (strike) …………………… on the 28th mission.
49. Yuri Gagarin (become) ……………………the first person in space when he (orbit) ……………………the Earth in a Vostok spacecraft on April 12, 1961.
50. While she (work) ……………………last week, the astronaut (realize) ……………………that she (need) ……………………a medium - size suit for spacewalking.
