Explain the method which can be used to separate wheat, sugar and stalks.

Explanation

First step (Winnowing) - Since the stalks are lighter than wheat and sugar, it is separated by winnowing. Stalks flies away from the winnower while sugar and wheat are left behind.
Second step (Sieving) - Since there is difference in size of wheat and sugar, sugar comes down through the sieve while wheat is left on the sieve.