[译] 直到20世纪中期太空时代开始时,宇航员这个词仍属于科学故事的范围。
[误] Till the beginning of the space age in the mid-20th century the word "astronaut" belonged to the realm of science fiction.

[正] Until the beginning of the space age in the mid-20th century the word "astronaut" belonged to the realm of science fiction.
[注] 介词(或连词) until, till 意义相同,可互换使用,只是句子开头不用 till,又如: Until now I know nothing about Pluto. 直到现在我对冥王星一无所知。/Until you told me, I had heard nothing of what happened. 直到你告诉我, 我才知道发生了什么事。