Answer: aperture (a)
Explanation: ok ill try my best to explain this
ISO can be thought of as the quality of the image
-higher the ISO, the grainer the image, but the more light the camera gets
-lower the ISO, the clearer the image, but the camera get less light. Best in outside or bright situations
-100 is the best ISO, but you can do 200
SHUTTER SPEED (S) can be thought of as well, shutter speed, which affects how light or dark and image is. Change this instead of ISO perferably.
-higher S, less bright, clearer image, faster shutter, you can take more photos at once
-lower S, more bright, can blur so if you go under 80 tripod is perfered.
APERTURE (A) can be thought of how blurred the background of an image is
-higher A, the less the background is bluured, more bright
-lower A, the more background is blurred, less bright
-for close ups I love going down as 1.4
-too close and you wont be able to take a photo, too far and you can't either
with aperture, you can increase depth of field
depth of field is how blurred the background is
to increase the depth of field you want to see more of the background, so increase the aperture (A)
should be corrrect, long explanation