Final answer:
Stored food in angiosperms, known as the endosperm, is produced after fertilization via a process called double fertilization, distinguishing them from gymnosperms.
Step-by-step explanation:
The stored food in angiosperms is formed after fertilization. This is in contrast to gymnosperms where pollination and fertilization do not result in a food storage tissue. In angiosperms, a unique event called double fertilization occurs. One sperm from the pollen fertilizes the egg, creating a diploid zygote, while the second sperm fuses with two polar nuclei to form a triploid cell.
This cell develops into the endosperm, which serves as the nutritive tissue for the developing embryo. Therefore, the correct answer to the student's question is e. formed after fertilization.