Harvest index is 100% for

Answer: Option A

Harvest index (HI) indicates and is referred to as the ratio of grain to total shoot dry matter and is a measure of reproductive efficiency.
It is calculated as:
$$\text{Harvest index}\left(\%\right)=\frac{\text{Grain yield}}{\text{Biological yield}}\times 100$$
The harvest index is 100% for fodders.