Double fertilization / Triple fusion is a characteristic of

The correct option is D Angiosperms
The process in which both nuclei from the pollen tube fuse is referred to as double fertilization. This is perhaps the most characteristic single feature of angiosperms and is not shared with any other group. Gymnosperms, in sharp contrast, have a multicellular female gametophyte, that consists of many hundreds or even thousands of cells. Double fertilization does not take place in this case, and the female gametophyte develops into the food-storage tissue of the seed.

Therefore, the correct answer is option D.