This task is about creating an unanswerable question based on a given passage. Construct a question that looks relevant to the given context but is unanswerable. Following are a few suggestions about how to create unanswerable questions:
(i) create questions which require satisfying a constraint that is not mentioned in the passage
(ii) create questions which require information beyond what is provided in the passage in order to answer
(iii) replace an existing entity, number, date mentioned in the passage with other entity, number, date and use it in the question
(iv) create a question which is answerable from the passage and then replace one or two words by their antonyms or insert/remove negation words to make it unanswerable.

Passage: Calvin Veltman undertook, for the National Center for Education Statistics and for the Hispanic Policy Development Project, the most complete study of English language adoption by Hispanophone immigrants. Mr Veltman's language shift studies document high bilingualism rates and subsequent adoption of English as the preferred language of Hispanics, particularly by the young and the native-born. The complete set of these studies' demographic projections postulates the near-complete assimilation of a given Hispanophone immigrant cohort within two generations. Although his study based itself upon a large 1976 sample from the Bureau of the Census (which has not been repeated), data from the 1990 Census tend to confirm the great Anglicization of the US Hispanic American origin population.
Who undertook the most complete study of Hispanic language adoption?