Proportional means that when you reduce the fractions, the two being compared will equal each other. Hope that helped. If you need more help i can try to explain better!
The answer is D. and I'll explain why. A proportion looks like this, 1/30. Or one over thirty. A proportion must be equal. Like 1/30 = 3/90. You must be able to multiply both by the same number, and then be able to scale it down to get the same thing. I know it sounds complicated, but it's really not. If you have any more comments, or questions, I'll be watching.
