The mother germ cells are transformed into a mature follicle through a series of steps. Provide the missing steps in the blank boxes.
$\boxed{\text{Oogonia}} \to \boxed{A} \to \boxed{\text{Primary follicle}} \to \boxed{B} \to \boxed{C} \to \boxed{\text{Mature or Graafian follicle}}$

(N/A) The process of follicular development in the ovary follows this sequence:
$1$. $\text{Oogonia}$ (Mother germ cells) undergo differentiation.
$2$. $A = \text{Primary oocyte}$ (surrounded by a layer of granulosa cells,forming the Primary follicle).
$3$. $\text{Primary follicle}$ develops further.
$4$. $B = \text{Secondary follicle}$ (formed by the addition of more layers of granulosa cells and a new theca layer).
$5$. $C = \text{Tertiary follicle}$ (characterized by a fluid-filled cavity called the antrum).
$6$. Finally,it matures into the $\text{Graafian follicle}$.