In which of the following plants, endosperm persists in the mature seed?

The correct option is D Castor
Endosperm is the triploid nutritive tissue that nourishes the developing embryo.

In some plants the endosperm is completely consumed by the developing embryo and hence the mature seed lacks endosperm. Such seeds are called non-albuminous or ex-albuminous seeds.
For example: pea, groundnut and beans.

In some plants the endosperm persists even after the seed matures. Such seeds are called albuminous seeds.
For example: castor and coconut.