I want to know the answer to the following question:
When did the US census start to allow residents to mark more than one ethno-racial identity on the census form?
All the background I'm provided with is that "Because more Americans have insisted on being allowed to acknowledge their mixed racial origins, the 2000 census for the first time allowed residents to check more than one ethno-racial identity and thereby identify as multiracial.". Is that enough to answer the question?