Which of the following describes a typical mature angiosperm embryo sac?

Identify the parts of the pistil labeled as $P$,$Q$,and $R$:
Receptive surface for pollen grains $- P$
Elongated slender part of the pistil $- Q$
Basal swollen part of the pistil $- R$
$\quad\quad\quad\quad P \quad\quad\quad Q \quad\quad\quad R$

In a majority of flowering plants,out of the four megaspores,........ megaspores degenerate and ........ megaspore remains functional.

The part of the gynoecium that receives the pollen is called:

Which cells together form the egg apparatus?

In a typical angiosperm,how many female gametophytes develop within a single megasporangium?