What does the filiform apparatus do at the entrance into the ovule?

Pollen grains can be stored for several years in liquid nitrogen having a temperature of (in $^oC$)

When the pollen tube enters the embryo sac,it enters through the ..... cells.

The movement of the pollen tube is called:

In angiosperms,the pollen tube enters the embryo sac through:

Identify the correct sequence of events of pollen-pistil interaction given below.
$(a)$ Pollen tube grows through the stigma,style and reaches the ovule.
$(b)$ Pollen grain lands on the stigma.
$(c)$ Pollen germinates to form pollen tube.
$(d)$ Pollen tube carrying $2$ male gametes enters the ovule.
Choose the correct option.