In industry, natural materials difficult to get are often replaced by plastics.
譯文：在工業中，不易獲得的天然材料常常被塑料代替。
Over the years, tools and technology themselves as a source of fundamental innovation have largely been ignored by historians and philosophers of science.
譯文：工具和技術本身作為根本性創新的源泉，多年來在很大程度上被歷史學家和科學的思想家忽視了。
Problems should be resolved in good time.
譯文：問題應該及時加以解決。
The Apollo Ⅻ crew reported that their spaceship was being followed by two UFOs.
譯文：阿波羅十二號的宇航員曾報告說，它們的宇宙飛船正遭到兩個不明飛行物的跟蹤。(用"遭到")
For separating iron from the impurities the iron ore must be melted.
