The correct answer is (a) drupe.
A drupe is a fruit that has a single seed surrounded by a fleshy outer layer and a hard inner layer. The outer layer is called the pericarp, and it is made up of three layers: the epicarp, the mesocarp, and the endocarp. The epicarp is the outermost layer, and it is usually the part of the fruit that we eat. The mesocarp is the middle layer, and it is usually fleshy and juicy. The endocarp is the innermost layer, and it is usually hard and woody.
The litchi fruit is a drupe. The outer layer of the litchi fruit is red or pink, and it is covered in small bumps. The flesh of the litchi fruit is white and juicy, and it has a sweet and slightly tart flavor. The seed of the litchi fruit is hard and brown.
The other options are not correct. A hesperidium is a type of citrus fruit, such as an orange or a grapefruit. A nut is a hard-shelled fruit that contains a single seed, such as a walnut or a pecan. A one-seeded berry is a type of berry that contains only one seed, such as a grape or a tomato.