What is the shape of stomata in grass leaves? 

Stomata are minute openings or pores that allow gaseous exchange. 
Stomata are typically found in plant leaves, yet they can likewise be present in certain stems.
At the point when it doesn't require carbon dioxide for photosynthesis, the plant closes these pores. Stomata in grass leaves are dumbbell shaped.
By diffusion, process gases exchange through stomata. Stomata have stomatal pores and guard cells.
With the help of a microscope, we can easily observe the stomata on the surface of leaves.
The movement (open & close) of the stomatal pores are controlled by the guard cells.

Hence, option B is the correct answer.