All protons in a vacuum have the same
1) speed
2) wavelength
3) energy
4) frequency

i guess that visual aids present persuasive examples to what you are presenting, some factors would be theme (does it fit with the color, information, what you are presenting), size (can you see it, is it a big enough span of data/information), and overall look of the visual aid.

hope this : )

d.7.5cm is your answer

answer///terminator or twilight zone;