Correct option is B
The component of the weir that divides the river width into weir portion and under sluice pocket is called the undersluice sill or the undersluice crest.
The undersluice sill is a low level portion of the weir that allows water to flow beneath it and provides an outlet for excess water. It is located downstream of the weir crest and above the under sluice openings, which are used to regulate the flow of water. The undersluice sill is designed to be lower than the weir crest to allow water to pass under it, while still maintaining a sufficient head of water over the weir crest to create a stable flow.
