Why is hand picking necessary after winnowing?

What is winnowing ?

Write about winnowing.

Oxygen is necessary for -

Hand picking method is effective in

People use a variety of methods to wash clothes. Usually after adding the soap, they ‘beat’ the clothes on a stone, or beat it with a paddle, scrub with a brush or the mixture is agitated in a washing machine. Why is agitation necessary to get clean clothes?

Why is ploughing of fields necessary before sowing seeds?

Why is it necessary to remove CO when ammonia is obtained by Haber's process?

Why is it necessary to remove CO when ammonia is obtained by Haber's process?

Which division is necessary to maintain constant chromosome number in all body cell of multicellular organism and why ?