A similarity between Ellis Island and Angel Island was that both immigration stations

served immigrants of mostly European descent

served immigrants of mostly Asian descent.

detained immigrants for weeks or months.

required immigrants to undergo questioning

A similarity between Ellis Island and Angel Island was that both immigration stations "required immigrants to undergo questioning."

While Ellis Island is located in New York and mostly serves European immigrants, Angel Island is located in San Francisco and mostly serves people from the Asian continent.However, there is a similarity in their functions, as both were immigration stations that questions and inspects the purpose of the immigrants coming to the United States.

Hence, in this case, the correct answer is option D "required immigrants to undergo questioning."

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