My mother was named Harriet Bailey. She was the daughter of Issac and Betsey Bailey, both coloured, and quite dark. My mother was of a darker complexion than either my grandmother or grandfather.
My father was a white man. He was admitted to be such by all I ever heard speak of my parentage. The opinion was also whispered that my master was my father; but of the correctness of this opinion, I know nothing; the means of knowing was withheld from me. My mother and I were separated when I was but an infant — before I knew her as my mother. It is a common custom, in the part of Maryland from which I ran away, to part children from their mothers at a very early age. Frequently, before the child has reached its twelfth month, its mother is taken from it, and hired out on some farm a considerable distance off, and the child is placed under the care of an older woman, too old for field labour. For what this separation is done, I do not know, unless it be to hinder the development of the child's affection towards its mother.
The author did not know exactly when he was born because______.

A. he did not know who his mother was.
B. there was no written evidence of it.
C. his master did not tell his father.
D. nobody on his farm knew anything about it.