How do plants regulate water loss due to transpiration?

Stomata are tiny pores present in the leaf that allows gas exchange and is where water vapour leaves plants and carbon dioxide enters. Special cells called guard cells present in the stomata, control each pore's opening or closing. When stomata are open, transpiration rates increase; when they are closed, transpiration rates decrease.

The stomata, stomata are pores in the leaf that allow gas exchange where water vapor leaves the plant and carbon dioxide enters.
 

I’m going to go with b!