Question

what opens and closes the stomata?
guard cells
vacuoles
chloroplasts

Explanation:

Guard cells are specialized cells that surround the stomata. They can change their shape (due to changes in turgor pressure) to open or close the stomata. Vacuoles are storage organelles, and chloroplasts are involved in photosynthesis; neither is responsible for opening/closing stomata.

Answer:

A. guard cells