Hey there!
The purpose of guard cells is to control the opening and closing of the Stomata, keeping it the correct width, or size.
Therefore, your correct answer would be Option 3, control the size of the Stomata.
Hope this helps!
It seems you forgot your options, but here are some things found in a chloroplast:
grana
Granal thylakoids
Stroma
Nukleloids (DNA rings)
Ribosomes
Starch granules
membranes
Now, some examples of thing NOT found in a chloroplast:
Endoplasmic Reticulum (that's another organelle)
The Milky Way is a spiral galaxy
hope this helps:)
2, because a theory is not a law that can not be changed, and new evidence can change a theory.
