One of the four students, A. B, C, and D, donated 1,000 yuan to the tsunami-stricken area. When asked by the teacher, they answered separately: A: The 1,000 yuan was not my donation. B: The 1,000 yuan was donated by D C: The 1,000 yuan was donated by B. D: The 1,000 yuan was not my donation. Only one of these four people told the truth, which shows who contributed the 1,000 yuan? ['A.', 'B.', 'C.', 'Ding.']