Stomata tend to close during the hot period and open during cooler hours in

Leaves surfaces have tiny pores on their surfaces called stomata. Stomata consist of guard cells and stomatal openings.

The guard cells around the stomatal opening tend to increase the temperature and Environmental changes, which control the stomatal opening. 

This likewise manages the gaseous exchange. This opening and closing further direct the water loss from the plant cells. In potato type, stomata stay open constantly, aside from certain hours at night. 

In the event of lucerne, stomata will generally close during the hot daytime and open during the cooler hours.

Hence, option D is the correct answer.