The correct option is D Mustard
Endosperm is a tissue produced inside the seeds of most flowering plants around the time of fertilization. It surrounds the embryo and provides nutrition in the form of starch, though it can also contain oils and protein. This can make endosperm a source of nutrition in human diet. A persistant endosperm is found in mustard, as in the caryopsis, the thin fruit wall is fused to the seed coat. Therefore, the nutritious part of the grain is the seed and its endosperm. In some cases the endosperm is selectively retained in food processing and the embryo and seed coat removed.
Thus, the correct answer is option D.