The duration of previous geologic periods was difficult to determine.
以前很难确定地质期的持续时间。
With such a long interval, it is difficult to determine the age of this fossil.
时间隔得这么久了,很难确定这化石的年代。
Outsiders may then find it difficult to determine your contributions and strengths.
局外人可能会很难确定你的贡献和优势。
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