There is really no grammatical, syntactical or lexical justification for Duo's requiring "the" in English. Vietnamese has no equivalent to the English definite article. It is true that we call the thing that is published every day "the newspaper" but "a newspaper" and "newspaper" can also answer the question, "What's that?" with reference to said item.
Tờ: accompanies a piece of paper or anything that resembles a piece of paper . I thought it would be in this case - 'a sheet of newspaper' but the correct answer was 'the newspaper'. The reason I guess my answer is incorrect is because 'a sheet of newspaper' requires 'mot to bao'.