First, he had to establish his credentials as a researcher.
首先，他得证明自己做调查员的资格。
交使节所递的国书,信任状
件;First, he had to establish his credentials as a researcher.
首先，他得证明自己做调查员的资格。
The ambassador presented her credentials to the monarch.
交
的证明书呈交国王。
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