同学你好，该知识点来自沪江网校《初中水平直达雅思6.5分【剑桥全能随到随学班】》的课程，想要更系统的学习，欢迎进入课程学习。不仅可以和更多的同学一起学习，而且还有老师、助教随时的学习指导和知识点解答哦。

同学你好~
21-28秒 but it was not until the rockets were invented in the late 1900s that people could begin to explore the space themselves.
It's not until ... that.. 是强调句，强调的是not until ...直到20c火箭被发明，人们才得以自己去太空探索
44-49秒 In 1959, the USSR sent the first man-made object to the moon  这里不是US，而是USSR（Union of Soviet Socialist Republics）苏联

祝学习愉快~