29.二十世纪七十年代初 in the early 1970s

28.环游世界去做报告

travel around the world to give lectures/

27.继续探索宇宙　

continue his exploration of the universe

26.梦想　 dream of

25.阻止某人做　 stop sb from doing

24.继续他的研究工作

go on with his research

23.为了做… in order to do

22.与…订婚 get/ be engaged to sb

21.活那么久　 survive that long

20.取得博士学位

much point in working on my PhD