To solve this problem, we need to identify the plant parts that consist of two generations, one within the other. Let's analyze each option:$\newline \bullet$(a) Pollen grains inside the anther:$\newline$ - Pollen grains represent the male gametophyte generation.$\newline$ - They develop within the anther, which is part of the sporophyte generation.$\newline$ - Therefore, this option consists of two generations, one within the other.$\newline \bullet$(b) Germinated pollen grain with two male gametes:$\newline$ - The germinated pollen grain is still part of the male gametophyte generation.$\newline$ - It does not represent two generations within each other.$\newline \bullet$(c) Seed inside the fruit:$\newline$ - The seed contains the embryo, which is the next sporophyte generation.$\newline$ - The fruit is part of the current sporophyte generation.$\newline$ - However, the seed itself does not contain two generations within each other.$\newline \bullet$(d) Embryo sac inside the ovule:$\newline$ - The embryo sac represents the female gametophyte generation.$\newline$ - It develops within the ovule, which is part of the sporophyte generation.$\newline$ - Therefore, this option consists of two generations, one within the other.$\newline$Based on the analysis, the correct options are:$\newline$(a) and (d).$\newline$This corresponds to Option 3.