Answer:
An Institutional Review Board (IRB) letter of approval from both the researcher's U.S. institution and an equivalent entity within the host country.
Explanation:
According to my research on Research and Development requisites in the US, I can say that based on the information provided within the question they must have An Institutional Review Board (IRB) letter of approval from both the researcher's U.S. institution and an equivalent entity within the host country.
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