I had known that my mother was sick as a result of a failing kidney, but I had not realized

A. Although I had known that my mother was suffering from a failing kidney, I had not realized my parents’ problems caused by this illness.

B. In my childhood I didn’t know my mother’s sickness, so I couldn’t realize how much trouble my parents had.

C. When I learned my mother’s sickness which was the result of a failing kidney, I realized the pain my mother had.

D. I hadn’t realized the problems they had to deal with until my parents told me about my mother’s illness.