As shown in the figure, it is a fan-shaped statistical chart of whether students in a class of Grade 8 know their parents' birthdays, where A stands for students who only know their fathers' birthdays

As shown in the figure, it is a fan-shaped statistical chart of whether students in a class of Grade 8 know their parents' birthdays, where A stands for students who only know their fathers' birthdays; B means C.

Test analysis: The number of people who know the mother's birthday is 40×55%=22.

So choose C.