文法問題發問... - 英檢

以下有幾題文法問題想請教版上高手

1. The A.(discovery of) helium in oil fields marked the beginning
B.(for doubt) in the C.(minds of) many geologists D.(in this
term) "fossil fuel".

答案是B. 想請教整句翻譯還有B應該要改成什麼答案才正確？

2. During their formation, diamonds, A.(the most hardest) material
known to science B.(need to be cooled) rapidly, C.(otherwise)
they D. (become) graphite.

答案是A. 請問A要改成什麼答案才正確？

3. The rail system A.(is) extensive in the Boston metropolitan area
B.(however) the service C.(will seem) much D.(least) rapid to
European and Japanese visitors.

答案是D. 請問D要改成什麼答案才正確？

4. Barge traffic, in France, A.(debuted) in the 19th centure, has
B.(steadily) decreased C.(in favor of) D.(trucking) firms.

答案是A. 請問A要改成什麼答案才正確？

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