Double fertilization is observed in .............

Identify $A, B, C$ and $D$ from the given diagram representing double fertilization in flowering plants.

What type of fertilization is observed in the plant shown in the figure?

Differentiate between the following:
$(i)$ Red algae and brown algae
$(ii)$ Liverworts and moss
$(iii)$ Homosporous and heterosporous pteridophytes
$(iv)$ Syngamy and triple fusion

Explain why sexual reproduction in angiosperms is said to take place through double fertilization and triple fusion? Also,provide a labelled diagram of the embryo sac to explain the phenomenon.

Number of nuclei taking part in double fertilization is