(N/A) The labels are as follows:
$A -$ Pollen grain
$B -$ Pollen tube
$C -$ Ovary
$D -$ Female germ cell (Egg cell)
$(b)$ Pollination is the process of transfer of pollen grains from the anther to the stigma of a flower.
Significance: It is essential for fertilization,as it brings the male gametes to the female reproductive part.
$(c)$ Fertilization in flowers occurs when a pollen grain lands on a suitable stigma and germinates to form a pollen tube. This tube grows through the style,carrying the male germ cell,and reaches the ovary. The male germ cell then fuses with the female germ cell present in the ovule to form a zygote.
$(i)$ Seed develops from the ovule.
$(ii)$ Fruit develops from the ovary.