Winnowing is used only for:
A.Homogeneous solid-solid mixtures
B.Homogeneous solid-liquid mixtures
C.Heterogeneous solid-liquid mixtures
D.Heterogeneous solid-solid mixtures

Hint: Winnowing means the separation of two heterogeneous solids, which can be defined by the separation of heavier substance from the lighter substance of a mixture using air or blowing air. It depended on the fact that mixture containing two components and one is heavier than another one, then it separated.

Complete step by step answer:
This is the technique to separate solids. If the mixture contains two solids which have different masses of particles, it would be separated by a winnowing method.
Most probably this method is used in agriculture which is developed by ancient cultures to separate grain from chaff.
The heterogeneous mixture is formed by two solid materials, there two materials separated from the mixture by the method of winnowing.

Therefore, Option (D) is the correct.

Additional information:
Winnowing is the process to separate heavier particles from the lighter particles of a mixture. This method is used by the farmers to separate lighter seed from heavier seeds of grains. This method is used to separate unpleasant husk from food.

Note:
Winnowing method used for the separate mixtures and particles. Basically, it is used in agriculture. This method is useful to the farmer to remove husk from the food. But in chemistry it used to separate two heterogeneous solid- solid mixtures which contain different masses of particles.