## Algebra 1: Common Core (15th Edition)

The wording of this question is a bit confusing, so let's break it down. A ratio is when one thing is divided by another thing. Because the problem states that there are different units in the ratio, we know that we have one unit in the numerator and a different unit in the denominator. Consider some examples: $\frac{60 miles}{hour}; \frac{9 gallons}{minute}; \frac{10 rotations}{day}$. These ratios tells us how quickly something is occurring, which is a rate, making D the correct answer.